- The importance of NO+(H2O)4 in the conversion of NO+(H2O)n to H3O +(H2O)n: I. Kinetics measurements and statistical rate modeling
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The kinetics for conversion of NO+(H2O)n to H3O+(H2O)n has been investigated as a function of temperature from 150 to 400 K. In contrast to previous studies, which show that the conversion goes completely through a reaction of NO +(H2O)3, the present results show that NO +(H2O)4 plays an increasing role in the conversion as the temperature is lowered. Rate constants are derived for the clustering of H2O to NO+(H2O)1-3 and the reactions of NO+(H2O)3,4 with H 2O to form H3O+(H2O)2,3, respectively. In addition, thermal dissociation of NO+(H 2O)4 to lose HNO2 was also found to be important. The rate constants for the clustering increase substantially with the lowering of the temperature. Flux calculations show that NO+(H 2O)4 accounts for over 99% of the conversion at 150 K and even 20% at 300 K, although it is too small to be detectable. The experimental data are complimented by modeling of the falloff curves for the clustering reactions. The modeling shows that, for many of the conditions, the data correspond to the falloff regime of third body association.
- Eyet, Nicole,Shuman, Nicholas S.,Viggiano, Albert A.,Troe, Juergen,Relph, Rachael A.,Steele, Ryan P.,Johnson, Mark A.
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- A convenient preparation of pentaaquanitrosylchromium(2+) sulfate: The crystal structure revisited
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The complex pentaaquanitrolsylchromium(2+) sulfate, [Cr(OH 2)5(NO)]SO4 has been prepared in a high yield by the hydrolysis of [Cr(NCCH3)5(NO)](BF4) 2 in dilute sulfuric acid. Crystals of [Cr(OH2) 5(NO)]SO4·H2O have been grown and characterized by X-ray crystallography. Continuous photolysis of [Cr(NCCH 3)5(NO)]2+ in acetonitrile solution with 404 nm light results in a release of NO with the quantum yield Φ = 0.55 mol einstein-1 at 298 K with the resulting solvated Cr2+ ion being trapped by molecular dioxygen present in the solution.
- D?ssing, Anders,Frey, Anne Mette
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- Production processes of H(D) atoms in the reactions of NO(A2Σ+) with C2H2, C2H4, H2O, and their isotopic variants
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The production of H(D) atoms was identified in the reactions of NO(A2Σ+) with C2H2, C2H4, H2O, and their isotopic variants. By measuring the Doppler profiles, the translational energies of H(D) atoms were determined. As for C2H2 and H2O, around 1/4 of the NO(A2Σ+) energy is partitioned into the translational mode, while the ratio is around 1/7 for C2H4. Such a large partitioning of the available energy into the translational mode cannot be explained by a C-H(O-H) bond rupture after an energy transfer. Nitrogen compounds, such as ONC2H and HONO, must be produced as pair products. The measured translational energies are much larger than those statistically expected, suggesting that the intermediate species are short-lived. No large isotope effect was observed in the average translational energies or in the relative yields. Quantum effects, such as tunneling, do not play important roles. Ab initio molecular orbital calculations were carried out to characterize these reactive processes. (C) 2000 Elsevier Science B.V.
- Umemoto, Hironobu,Terada, Naoki,Tanaka, Kunikazu,Takayanagi, Toshiyuki,Kurosaki, Yuzuru,Yokoyama, Keiichi
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- OH overtone spectra and intensities of pernitric acid
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The integrated absorption intensities of the 3νOH overtone transitions of the OH stretch of pernitric acid (HO2NO2) and nitric acid (HONO2) were measured in concentrated sulfuric acid (H2SO4) solution. As well, oscillator strengths for the OH overtones of isolated HO2NO2 were calculated ab initio. Both results indicate that the OH overtones of HO2NO2 have larger oscillator strengths than the corresponding transitions in HONO2 (1.3±0.5 times greater in H2SO4 solution; about 2 times greater according to the ab initio calculations). Overtone-induced photodissociation of HO2NO2 could play a role in HOx production at high solar zenith angles.
- Fono, Lorien,Donaldson,Proos, Robert J.,Henry, Bryan R.
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- Fine tuning the reactivity of corrole-based catalytic antioxidants
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In order to determine the electronic factors that may affect the catalytic antioxidant activity of water-soluble metallocorroles a series of 10-aryl-5,15-pyridinium manganese(III) corroles was prepared. These complexes were examined regarding the effect of the C10 substituent on the MnIV/MnIII redox potentials, catalytic rate constants for decomposition of HOONO, prevention of tyrosine nitration, and superoxide dismutase activity. This structure-activity relationship investigation provides new insight regarding the mechanism by which manganese(III) corroles act as catalytic antioxidants. It also discloses the superiority of the C 10-anysil-substituted complex in all examined aspects.
- Okun, Zoya,Gross, Zeev
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- Potential role of the nitroacidium ion on HONO emissions from the snowpack
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The effects of photolysis on frozen, thin films of water-ice containing nitrogen dioxide (as its dimer dinitrogen tetroxide) have been investigated using a combination of Fourier transform reflection - absorption infrared (FT-RAIR) spectroscopy and mass spectrometry. The release of HONO is ascribed to a mechanism in which nitrosonium nitrate (NO+NO3 -) is formed. Subsequent solvation of the cation leads to the nitroacidium ion, H2ONO+, i.e., protonated nitrous acid. The pathway proposed explains why the field measurement of HONO at different polar sites is often contradictory.
- Hellebust, Stig,Roddis, Tristan,Sodeau, John R.
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- Crystal structure, optical, magnetic, and photochemical properties of the complex pentakis(dimethyl sulfoxide)nitrosylchromium(2+) hexafluorophosphate
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The nitrosyl complex [Cr(dmso)5(NO)](PF6)2 (1) (dmso = dimethyl sulfoxide) has been prepared by the solvolysis of [Cr(NCCH3)5(NO)](PF6)2 in neat dmso. The optical absorption spec
- Dethlefsen, Johannes W.,D?ssing, Anders,Kadziola, Anders
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- Near-UV Absorption Cross Sections and Trans/Cis Equilibrium of Nitrous Acid
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The A 1A'' X 1A' absorption spectrum of gaseous nitrous acid has been measured in the 300-400-nm range.Absolute cross sections were determined by a combination of gas-phase and wet chemical analysis.The cross sections of prominent bands are 25percent larger than the recommended values of Stockwell and Calvert.The influence of spectral resolution on absolute and differential absorption cross sections was also investigated.The integrated band area of the n?* transition yields an oscillator strength f = (8.90 +/- 0.36) x 10-4, less than the reported liquid phase value of 2 x 10-3.The equilibrium constant K = ptrans/pcis, base d on the assumption that the oscillator strength of the n?* transition is the same for both rotamers, was found to be 3.25 +/- 0.30 at 277 K.This yields an energy difference ΔE between trans- and cis-HONO of -2700 J mol-1 in the electronic ground state, and -6000 J mol-1 in the excited state.
- Bongartz, A.,Kames, J.,Welter, F.,Schurath, U.
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- Role of OH-stretch/torsion coupling and quantum yield effects in the first OH overtone spectrum of cis-cis HOONO
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The effects of OH-stretch/HOON torsion coupling and of quantum yield on the first OH overtone spectrum of cis-cis HOONO were investigated. The direct absorption spectrum of cis-cis HOONO was recorded by cavity ringdown spectroscopy in a discahrge flow cell. A single band of HOONO is observed at 6370 cm-1 and is assigned as the origin of the first OH overtone of cis-cis HOONO. The results show that the coupling of the OH stretch to the HOON torsion and quantum yield effects are primarily responsible for the features seen in the action spectrum.
- McCoy, Anne B.,Fry, Juliane L.,Francisco, Joseph S.,Mollner, Andrew K.,Okumura, Mitchio
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- Experimental and theoretical study of the reaction of HO- with NO
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Hydroxide ion (HO-) reacts with nitric oxide by slow reactive electron detachment with a rate coefficient ca. 4 x 10-12 cm3 s-1 at 298 K.The detachment process is presumably associative detachment forming nitrous acid and an electron.Observations, data analysis, and alternative explanations for these observations are discussed.The associative detachment reaction was also investigated theoretically through calculations of the geometries, relative energies, and normal-mode vibrational frequencies of the relevant species HO-, HO, NO, cis- and trans-HONO, and cis- and trans-HONO-.These calculations indicate that in the ion HONO-, the cis conformer is more stable, while in the neutral HONO, the trans conformer is more stable.The HO-NO bond in HONO, which is formed in this reaction, is much stronger than the HO--NO bond in HONO- with an energy of 198.7+/-1.8 kJ mol-1 for cis HONO and 52.2+/-5 kJ mol-1 for cis-HONO- at 0 K.HONO- is bound with respect to HONO.The adiabatic electron detachment energy resulting from detachment from cis-HONO- forming the same conformer of the neutral molecule cis-HONO is 0.29+/-0.05 eV.The HO-NO equilibrium bond distance in HONO- is considerably longer than that in HONO, with values of 1.750 and 1.640 Angstroem for trans- and cis- HONO-, respectively, and 1.429 and 1.392 Angstroem for trans- and cis-HONO, respectively.These geometric and energetic characteristics of HONO- and HONO are combined with calculations of relative energies of these species at nonequilibrium/distorted HO-NO bond lengths to give a qualitative picture of the potential energy curves for these species along the reaction coordinate.While no significant energy barrier to autodetachment of HONO- is present, the Franck-Condon wave function overlap for aitodetachment is small and is likely the reason for the observed inefficiency.The maximum calculated rate constant for associative detachment is 4 x 10-12 cm3 s-1, in good agreement with the observed value.
- Doren, Jane M. Van,Viggiano, A. A.,Morris, Robert A.,Miller, Amy E. Stevens,Miller, Thomas M.,et al.
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- Infrared matrix isolation and theoretical studies of the hydrogen bonded complexes between nitrous acid and 1,1-dichloroethylene
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The complexes formed between trans and cis isomers of nitrous acid and 1,1-dichloroethylene (1,1-DCE) in argon matrixes have been identified and characterized by help of FTIR spectroscopy. The experimental spectra evidenced that trans- and cis-HONO isomer
- Olbert-Majkut, Adriana,Mielke, Zofia
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- Heterogeneous chemistry of HONO on liquid sulfuric acid: A new mechanism of chlorine activation on stratospheric sulfate aerosols
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Heterogeneous chemistry of nitrous acid (HONO) on liquid sulfuric acid (H2SO4) was investigated at conditions that prevail in the stratosphere. The measured uptake coefficient (γ) of HONO on H2SO4 increased with
- Zhang, Renyi,Leu, Ming-Taun,Keyser, Leon F.
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- Heterogeneous reaction of NO2 on fresh and coated soot surfaces
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The heterogeneous reaction of nitrogen dioxide (NO2) on fresh and coated soot surfaces has been investigated to assess its role in night-time formation of nitrous acid (HONO) in the atmosphere. Soot surfaces were prepared by incomplete combustion of propane and kerosene fuels under lean and rich flame conditions and then processed by heating to evaporate semivolatile species or by coating with pyrene, sulfuric acid, or glutaric acid. Uptake kinetics and HONO yield measurements were performed in a low-pressure fast-flow reactor coupled to a chemical ionization mass spectrometer (CIMS), using atmospheric-level NO2 concentrations. The uptake coefficient and the HONO yield upon interaction of NO2 with nascent soot depend on the type of fuel and combustion regime and are the highest for samples prepared using fuel rich flame. Heating the nascent soot samples before exposure to NO2 removes the organic material from the soot backbone, leading to a significant increase in NO2 uptake coefficient and HONO yield. Continuous exposure to NO2 reduces the reactivity of soot because of irreversible deactivation of the surface sites. Our results support the oxidation-reduction mechanism involving adsorptive and reactive centers on soot surface where NO2 is converted to HONO and other products. Coating of the soot surface by different materials to simulate atmospheric aging has a strong impact on its reactivity toward NO2 and the resulting HONO production. Coating of pyrene has little effect on either reaction rate or HONO yield. Sulfuric acid coating does not alter the uptake coefficient, but significantly reduces the amount of HONO formed. Coating of glutaric acid significantly increases NO2 uptake coefficient and HONO yield. The results of our study indicate that the reactivity and HONO generating capacity of internally mixed soot aerosol will depend on the chemical composition of the coating material and hence will vary considerably in different polluted environments.
- Khalizov, Alexei F.,Cruz-Quinones, Miguel,Zhang, Renyi
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- Heterogeneous reaction of NO2 on hexane soot: A Knudsen cell and FT-IR study
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NO2 can react with soot particles to produce HONO. The heterogeneous reaction of NO2 on freshly prepared hexane soot was investigated using a Knudsen cell reactor and FTIR spectroscopy. Initial uptake coefficients were determined using gas-diffusion models that take into consideration the surface area of the top layer of soot particles as well as the accessible underlying layers of soot particles. Under dry conditions, the initial uptake coefficient was near 5 x 10-5 at a gas concentration of 2.5 x 1011 molecules/cc and 295 K. The adsorbed products remained on the surface in agreement with previous results. HONO was a gas-phase reaction product, accounting for 36% of the NO2 reacted. Knudsen cell data were in better agreement with the values of the uptake coefficient determined from other experimental methods when the BET areas of the soot samples were taken into account and average values of the uptake coefficient were compared.
- Al-Abadieh, Hind A.,Grassian
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- OH(A) Production in the 193-nm Photolysis of HONO
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The formation of OH(A) and OD(A) in the 193-nm photolyses of HONO and DONO with a low quantum yield of about 10-5 is reported.The rotational population of OH(A) can be approximated by a Boltzmann distribution with a temperature of 650 K.It is compared with the predictions of the impulsive and statistical models and is found to be close to the latter.A reinvestigation of the absorption spectrum for HONO between 185 and 270 nm and a comparison of the OH(A-X) fluorescence intensities excited in the 193-nm photolyses of nitric and nitrous acids are also reported.
- Kenner, R. D.,Rohrer, F.,Stuhl, F.
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- Measurement of absolute absorption cross sections for nitrous acid (HONO) in the near-infrared region by the continuous wave cavity ring-down spectroscopy (cw-CRDS) technique coupled to laser photolysis
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Absolute absorption cross sections for selected lines of the OH stretch overtone 2ν1 of the cis-isomer of nitrous acid HONO have been measured in the range 6623.6-6645.6 cm-1 using the continuous wave cavity ring-down spectroscopy (cw-CRDS) technique. HONO has been generated by two different, complementary methods: in the first method, HONO has been produced by pulsed photolysis of H2O2/NO mixture at 248 nm, and in the second method HONO has been produced in a continuous manner by flowing humidified N2 over 5.2 M HCl and 0.5 M NaNO2 solutions. Laser photolysis synchronized with the cw-CRDS technique has been used to measure the absorption spectrum of HONO produced in the first method, and a simple cw-CRDS technique has been used in the second method. The first method, very time-consuming, allows for an absolute calibration of the absorption spectrum by comparison with the well-known HO2 absorption cross section, while the second method is much faster and leads to a better signal-to-noise ratio. The strongest line in this wavelength range has been found at 6642.51 cm-1 with σ = (5.8 ± 2.2) × 10-21 cm2.
- Jain, Chaithanya,Morajkar, Pranay,Schoemaecker, Coralie,Viskolcz, Bela,Fittschen, Christa
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- A synergetic effect in nitrous acid formation by sonolysis of nitric acid in the presence of nitrous oxide
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A synergetic effect is found in the sonochemical formation of HNO2 in HNO3 solution in the presence of an N2O-Ar gaseous mixture. The maximum rate of HNO2 formation is observed at an N2O : Ar ratio of 15 : 85 (v/v). During the sonolysis of 4 M HNO3 solutions, the rate of HNO2 formation increases multifold due to the synergetic effect. The rate of sonochemical hydrazine decomposition in nitrate solutions also increases considerably in the presence of N2O.
- Nikitenko,Seliverstov
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- A Novel Moving Boundary Reaction involving Hydroxylamine and Nitric Acid
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An initially homogeneous solution of hydroxylamine in nitric acid can react to form a two-layer system, a layer of nitrous acid in nitric acid above a layer of hydroxylamine in nitric acid, with a sharp boundary between them that moves steadily downwards.
- Gowland, Rory,Stedman, Geoffrey
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- Heterogeneous interaction and reaction of HONO on ice films between 173 and 230 K
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Both the heterogeneous interaction of HONO on the ice surface and the heterogeneous reaction of HONO with HBr on the ice surface have been investigated in a flow reactor interfaced with a differentially pumped quadrupole mass spectrometer. The surface uptake amount and initial uptake coefficient of HONO on the ice surface were determined as a function of the ice-film temperature between 173 and 205 K. The reaction probability of HONO over the HBr-treated ice surfaces has been determined as a function of HBr partial pressures at 190K, 200K, and 230K, respectively. The reaction mechanism is proposed and discussed. Kinetic analysis indicates that the heterogeneous reaction of HONO with HBr on ice surfaces follows the Eley-Rideal type.
- Chu, Liang,Diao, Guowang,Chu, Liang T.
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- Reaction Kinetics of Nitrogen Dioxide with Liquid Water at Low Partial Pressure
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The reaction 2NO2(g) + H2O(l) ---> 2H+ + NO3- + NO2- (1) has been studied for 1E-7 NO2 a reactant from the gas into the aqueous phase, the rate depends upon the following: (a) physical mass transfer of the reactant, (b) the equilibrium solubility of NO2, and (c) homogeneous aqueous-phase kinetics.In order for the observed rate to yield information most sensitive to (c), the rate of (a) must be comparable to that of (c).In the case of a second-order reaction, this can be achieved by working at low partial pressure of NO2 as well as a high rate of physical mixing of the two phases.To facilitate the latter, the gas was brought into contact with the liquid as finely dispersed bubbles produced by flowing through a disc-frit; the mass transfer time constant, determined by uptake of CO2, was τm = 1.7 - 5.3 s.The rate of reaction 1, monitored by observing the electrical conductivity of the aqueous solution, exhibited dependence on pNO2 and τm consistent with second-order kinetics and a steady-state aqueous-phase NO2 concentration.Values of HNO2, the Henry's law coefficient, and k1, the second-order aqueous-phase rate constant, were determined to be (7.0+/-0.5)E-3 M atm-1 and (1.0+/-0.1)E8 M-1 s-1, respectively, at 22 deg C.Self-consistency of the gas-liquid reaction model has been demonstrated in terms of the identity of the diffusing species and the extent of mass-transport limitation.
- Lee, Y.-N.,Schwartz, S.E.
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- Radical-Molecule Kinetics in Pulsed Uniform Supersonic Flows: Termolecular Association of OH + NO between 90 and 220 K
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The low-temperature dependence of the temolecular association reaction of OH with NO employing N2 as the third body has been investigated using a new pulsed uniform supersonic expansion flow reactor.The absolute low-pressure reaction rate coefficient is reported for the temperature range 90-220 K.The temperature dependence of the rate coefficient for this reaction is found to be well fit by k=(7.0 +/-2.0)E-31(T/300)-2.6 +/-0.3 cm6s-1.The results agree with those obtained in the higher temperature regime and with RRKM predictions of the rate coefficient both validating the new technique and providing valuable information on the extended temperature dependence of this atmospherically relevant reaction.
- Atkinson, Dean B.,Smith, Mark A.
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- Radiation-induced Reactions of (2-Methyl-5-nitro-1H-imidazole-1-ethanol)nickel(II) in Aqueous Solution: A Flash-photolysis and Steady-state Gamma-radiolysis Study
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On gamma radiolysis of the nickel(II) complex of metronidazole (2-methyl-5-nitro-1H-imidazole-1-ethanol), hydroxyl radicals and the hydrated electron e(1-) (aq) react with the complex leading to the destruction of the nitroimidazole structure.The loss of the complex and the production of nitrite have been followed by steady-state experiments, while the transient kinetics of the hydroxyl reactions have been probed by flash photolysis.The OH radicals react with the complex with a rate constant of ca. 4.0E9 dm3 mol-1 s-1, resulting in elimination of the nitro groupeither by adding to the C5 position or through generation of a nickel(III) species.The latter undergoes intramolecular electron transfer from the ring with a rate constant of ca. (4.6 +/- 0.4)E3 s-1, while the imidazole radicals formed decay by second-order kinetics with a 2k/ε value of (9.1 +/- 1.3)E5 cm s-1.The hydrated electrons generate the nitroanion radicals, a fraction of which undergoes denitration while the rest is reduced by a successive four-electron scheme to a hydroxylamino derivative.
- Roy, Maitrayee Basu,Mandal, Parikshit C.,Bhattacharyya, Sudhindra N.
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- Infrared absorption cross-section measurements for nitrous acid (HONO) at room temperature
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Infrared absorption cross sections for nitrous acid (HONO) were measured using HONO spectra recorded simultaneously by UV/visible and FTIR spectroscopy. HONO was prepared by the reaction of HCl(g) and NaNO2(s) and was introduced into a 561 L environmental chamber equipped with parallel sets of White optics with total path 52.5 m for UV/visible and FTIR spectroscopy. Alternatively, HONO was prepared in situ by reaction of ClNO(g) with water vapor. Absolute concentrations of HONO were determined independently using the UV spectrum and published UV absorption cross sections. All experiments were carried out at 750 Torr total pressure in N2 at 294-297 K. We report both Q-branch intensities and integrated absorbances for the HONO modes trans-v3 (1263 cm-1), cis-v4 (852 cm-1), and trans-v4 (790 cm-1). For trans-v3 and cis-v4 we also include synthetic reference spectra composed of Gaussian functions which give an accurate reproduction of our experimental references, and can easily be generated by computer for ease of use in other laboratories.
- Barney, William S.,Wingen, Lisa M.,Lakin, Matthew J.,Brauers, Theo,Stutz, Jochen,Finlayson-Pitts, Barbara J.
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- Interaction of NO2 with hydrocarbon soot: Focus on HONO yield, surface modification, and mechanism
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Using a coated-wall flow tube connected to a mass spectrometer, the heterogeneous conversion of NO2 to HONO on dry hydrocarbon soot surfaces has been studied at room temperature and 243 K. Particular attention was given to the measurement of the HONO yield as a function of hydrocarbon fuel, NO2 partial pressure, extent of uptake, and surface oxidation state. In all cases, the yield is invariant of these parameters and close to unity, indicative of an irreversible oxidation mechanism by which the NO 2 abstracts an H atom from the surface. XPS analysis shows that the surface N content does not measurably increase with NO2 exposure. There is minimal surface reactivity regeneration with time or via exposure to high relative humidity. A BET surface area measurement of the entire soot film exposed to NO2 was used to determine the amount of HONO that can be generated from the soot surface per unit surface area, prior to its deactivation. The reduction of NO2 to HONO on soot is unlikely to account for the observed nighttime buildup of HONO in polluted urban environments.
- Aubin, Daniel G.,Abbatt, Jonathan P. D.
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- New experimental and theoretical approach to the heterogeneous hydrolysis of NO2: Key role of molecular nitric acid and its complexes
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Although heterogeneous chemistry on surfaces in the troposphere is known to be important, there are currently only a few techniques available for studying the nature of surface-adsorbed species as well as their chemistry and photochemistry under atmospheric conditions of 1 atm pressure and in the presence of water vapor. We report here a new laboratory approach using a combination of long path Fourier transform infrared spectroscopy (FTIR) and attenuated total reflectance (ATR) FTIR that allows the simultaneous observation and measurement of gases and surface species. Theory is used to identify the surface-adsorbed intermediates and products, and to estimate their relative concentrations. At intermediate relative humidities typical of the tropospheric boundary layer, the nitric acid formed during NO2 heterogeneous hydrolysis is shown to exist both as nitrate ions from the dissociation of nitric acid formed on the surface and as molecular nitric acid. In both cases, the ions and HNO3 are complexed to water molecules. Upon pumping, water is selectively removed, shifting the NO3--HNO 3(H2O)y, equilibria toward more dehydrated forms of HNO3 and ultimately to nitric acid dimers. Irradiation of the nitric acid-water film using 300-400 nm radiation generates gaseous NO, while irradiation at 254 nm generates both NO and HONO, resulting in conversion of surface-adsorbed nitrogen oxides into photochemically active NOx, These studies suggest that the assumption that deposition or formation of nitric acid provides a permanent removal mechanism from the atmosphere may not be correct. Furthermore, a potential role of surface-adsorbed nitric acid and other species formed during the heterogeneous hydrolysis of NO2 in the oxidation of organics on surfaces, and in the generation of gas-phase HONO on local to global scales, should be considered.
- Ramazan,Wingen,Miller,Chaban,Gerber,Xantheas,Finlayson-Pitts
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- Beyond esterase-like activity of serum albumin. Histidine-(nitro)phenol radical formation in conversion cascade of p-nitrophenyl acetate and the role of infrared light
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Serum albumin, recognized mainly for its capacity to act as a carrier protein for many compounds, can also actively transform some organic molecules. As a starting point in this study, we consider esterase-like activity of bovine serum albumin (BSA) toward p-nitrophenyl acetate (p-NPA). Our results reveal that the reaction goes beyond ester hydrolysis step. In fact, the transformation product, p-nitrophenol (p-NP), becomes a substrate for further reaction with BSA in which its nitro group in subtracted and released in the form of HNO2. Spectral data indicate that this cascade of events proceeds through formation of phenoxyl radical via proton-coupled electron transport (PCET) between OH group of p-NP and imidazole ring of histidine from the protein. Furthermore, the effect of application of electromagnetic radiation in the infrared range suggests that this remote physical trigger can support interactions based on PCET mechanism by acting on polarization and mutual alignment of water dipoles serving as effective water wires.
- Kowacz, Magdalena,Warszyński, Piotr
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- Probing the Reaction Mechanisms Involved in the Decomposition of Solid 1,3,5-Trinitro-1,3,5-triazinane by Energetic Electrons
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The decomposition mechanisms of 1,3,5-trinitro-1,3,5-triazinane (RDX) have been explored over the past decades, but as of now, a complete picture on these pathways has not yet emerged, as evident from the discrepancies in proposed reaction mechanisms and the critical lack of products and intermediates observed experimentally. This study exploited a surface science machine to investigate the decomposition of solid-phase RDX by energetic electrons at a temperature of 5 K. The products formed during irradiation were monitored online and in situ via infrared and UV-vis spectroscopy, and products subliming in the temperature programmed desorption phase were probed with a reflectron time-of-flight mass spectrometer coupled with soft photoionization at 10.49 eV (ReTOF-MS-PI). Infrared spectroscopy revealed the formation of water (H2O), carbon dioxide (CO2), dinitrogen oxide (N2O), nitrogen monoxide (NO), formaldehyde (H2CO), nitrous acid (HONO), and nitrogen dioxide (NO2). ReTOF-MS-PI identified 38 cyclic and acyclic products arranged into, for example, dinitro, mononitro, mononitroso, nitro-nitroso, and amines species. Among these molecules, 21 products such as N-methylnitrous amide (CH4N2O), 1,3,5-triazinane (C3H9N3), and N-(aminomethyl)methanediamine (C2H9N3) were detected for the first time in laboratory experiments; mechanisms based on the gas phase and condensed phase calculations were exploited to rationalize the formation of the observed products. The present studies reveal a rich, unprecedented chemistry in the condensed phase decomposition of RDX, which is significantly more complex than the unimolecular gas phase decomposition of RDX, thus leading us closer to an understanding of the decomposition chemistry of nitramine-based explosives.
- Singh, Santosh K.,Zhu, Cheng,Vuppuluri, Vasant,Son, Steven F.,Kaiser, Ralf I.
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p. 9479 - 9497
(2019/11/11)
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- Phototransformation of 5-nitro-2-furaldehyde in aqueous solution. A laser flash photolysis and product analysis study
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Laser flash photolysis of 5-nitro-2-furaldehyde (NFA) in solution shows a short-lived transient absorption with λmax = 475 ± 5 nm, which is relatively insensitive to solvent polarity and is assigned to the lowest triplet state of NFA (3NFA?). In water, the 3NFA? absorption decays to a long-lived absorption, the study of which, at different times after the end of the laser pulse, reveals it to be due to a furyloxyl radical (λmax ≈ 375 nm) and to the radical anion NFA- (λmax ≈ 400 nm). These radicals were produced independently to confirm the assignment. The lifetime of 3NFA? depends both on the solvent and the ground-state concentration of NFA. An (n, π?) nature is attributed to 3NFA? on the basis of the propensity of 3NFA? to abstract a hydrogen-atom from the solvent. Kinetic evidence for triplet excimer formation was obtained from the self-quenching of 3NFA? in solvents where the triplet decay is slower. The effect of acidity on the triplet lifetime is discussed with respect to an electron-transfer self-quenching mechanism, assisted by the triplet excimer which is proposed to dissociate into radical ions. Chromatographic and spectroscopic analysis of the photolysed aqueous solution of NFA enabled the identification of 5-hydroxymethylene-2(5H)-furanone, nitrite ion and an unknown substance as the major photoproducts. Conclusive evidence is presented that the observed 5-hydroxymethylene-2(5H)-furanone is formed from the furyloxyl radical. It is shown that the unknown substance can also be obtained from both the photoreduction of NFA in propan-2-ol and chemical reduction of NFA by Fe(s) in water (along with 5-amino-2-furaldehyde). Based on 1H- and 13C-NMR (with 2-D HMQC) and vibrational absorption spectroscopy, a tentative structure is proposed for the substance of tR 3.69 minutes obtained as a photoreduction product of NFA in water. Inorganic anions are shown to be one-electron oxidised by 3NFA? (as indicated by the observation of both the radical anion of NFA and the inorganic radical) with second-order rate constants being dependent on E17 of the inorganic radical. The implications of the results from complete quenching of 3NFA? by inorganic anions, and subsequent product analysis, for the phototransformation mechanism of NFA in water are discussed.
- Martins, Luis J.A.,Ferreira, Jo?o M. M.
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p. 721 - 735
(2017/07/07)
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- Investigations on HONO formation from photolysis of adsorbed HNO3 on quartz glass surfaces
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During the last few decades, nitrous acid (HONO) has attracted significant attention as a major source of the OH radical, the detergent of the atmosphere. However, the different daytime sources identified in the laboratory are still the subject of controversial discussion. In the present study, one of these postulated HONO sources, the heterogeneous photolysis of nitric acid (HNO3), was studied on quartz glass surfaces in a photo flow-reactor under atmospherically relevant conditions. In contrast to other investigations, a very low HNO3 photolysis frequency for HONO formation of J(HNO3 → HONO) = 2.4 × 10-7 s-1 (0° SZA, 50% r.h.) was determined. If these results can be translated to atmospheric surfaces, HNO3 photolysis cannot explain the significant HONO levels in the daytime atmosphere. In addition, it is demonstrated that even the small measured yields of HONO did not result from the direct photolysis of HNO3 but rather from the consecutive heterogeneous conversion of the primary photolysis product NO2 on the humid surfaces. The secondary NO2 conversion was not photo-enhanced on pure quartz glass surfaces in good agreement with former studies. A photolysis frequency for the primary reaction product NO2 of J(HNO3 → NO2) = 1.1 × 10-6 s-1 has been calculated (0° SZA, 50% r.h.), which indicates that renoxification by photolysis of adsorbed HNO3 on non-reactive surfaces is also a minor process in the atmosphere.
- Laufs, Sebastian,Kleffmann, J?rg
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p. 9616 - 9625
(2016/04/19)
-
- Absorption and Oxidation of Nitrogen Oxide in Ionic Liquids
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A new strategy for capturing nitrogen oxide, NO, from the gas phase is presented. Dilute NO gas is removed from the gas phase by ionic liquids under ambient conditions. The nitrate anion of the ionic liquid catalyzes the oxidation of NO to nitric acid by atmospheric oxygen in the presence of water. The nitric acid is absorbed in the ionic liquid up to approximately one mole HNO3per mole of the ionic liquid due to the formation of hydrogen bonds. The nitric acid can be desorbed by heating, thereby regenerating the ionic liquid with excellent reproducibility. Here, time-resolved in-situ spectroscopic investigations of the reaction and products are presented. The procedure reveals a new vision for removing the pollutant NO by absorption into a non-volatile liquid and converting it into a useful bulk chemical, that is, HNO3.
- Kunov-Kruse, Andreas J.,Thomassen, Peter L.,Riisager, Anders,Mossin, Susanne,Fehrmann, Rasmus
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p. 11745 - 11755
(2016/08/05)
-
- Absorption cross sections of 2?Nitrophenol in the 295?400 nm region and photolysis of 2?Nitrophenol at 308 and 351 nm
-
2-Nitrophenol is an important component of “brown carbon” in the atmosphere. Photolysis is its dominant gas phase removal process. We have determined the gas phase absorption cross sections of 2-nitrophenol in the 295?400 nm region by using cavity ring-down spectroscopy. 2-Nitrophenol exhibits a broad absorption band over the wavelength region studied, with the peak absorption located at 345 nm. Absorption cross section values range between (2.86 ± 0.18) × 10?18 and (2.63 ± 0.31) × 10?20 cm2/ molecule over the 295?400 nm range. We have investigated the HONO, NO2, and OH formation channels following the gas phase photolysis of 2-nitrophenol at 308 and 351 nm. Direct NO2 formation was not observed. HONO and OH are direct products from 2-nitrophenol photolysis. The average OH quantum yields from the photolysis of 0.5, 1.0, and 2.0 mTorr of 2-nitrophenol are 0.69 ± 0.07 and 0.70 ± 0.07 at 308 and 351 nm. The average HONO quantum yields are 0.34 ± 0.09 and 0.39 ± 0.07 at 308 and 351 nm. The OH and HONO quantum yields are independent of nitrogen carrier gas pressure in the 20?600 Torr range. Oxidant formation rate constants from 2-nitrophenol photolysis have been calculated. Discussions have been made concerning the role of 2-nitrophenol gas phase photolysis in the formation of atmospheric oxidants in regions of high anthropogenic emissions.
- Sangwan, Manuvesh,Zhu, Lei
-
p. 9958 - 9967
(2018/04/27)
-
- Photolysis of nitric acid at 308 nm in the absence and in the presence of water vapor
-
We have re-examined the NOx channels from the 308 nm gas-phase photolysis of nitric acid (HNO3) by using excimer laser photolysis combined with cavity ring-down spectroscopy. The photolysis products were monitored in the 552-560 and 640-648 nm regions. Direct comparison of the photolysis product spectrum in the 640-648 nm region with literature vibronic band origins and line intensities in electronically excited NO2 (NO2) suggests that NO2 is not formed from HNO3 photolysis at 308 nm. A comparison of the photolysis product spectrum in the 552-560 nm region with a standard NO2 spectrum indicates that ground-state NO2 is a photolysis product. We have determined the NO2 quantum yield from the 308 nm HNO3 photolysis. We also investigated HNO3 photolysis in the presence of water vapor. For equilibrated HNO3/H2O mixtures, we did not observe significant variation of product absorption around 552 nm with delay times between the firing of the photolysis and the probe lasers. Transient product absorption measurements at 342.0 and 343.5 nm (respective wavelengths where the peak and valley of HONO absorptions are located) are consistent with ground-state NO2 being the predominant NOx product from the 308 nm photolysis of a HNO3/H2O mixture. Atmospheric implications are also discussed.
- Zhu, Lei,Sangwan, Manuvesh,Huang, Li,Du, Juan,Chu, Liang T.
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p. 4907 - 4914
(2015/06/02)
-
- Natural kaolin derived stable SBA-15 as a support for Fe/BiOCl: A novel and efficient Fenton-like catalyst for the degradation of 2-nitrophenol
-
The ordered mesoporous material SBA-15 (FCSBA-15) with an enhanced hydrothermal stability was successfully synthesized from natural kaolin in the presence of a fluorocarbon surfactant. FCSBA-15 was further used as the support for Fe/BiOCl with the aim of exploring its Fenton-like catalytic performance toward the degradation of 2-nitrophenol. Based on characterization techniques including X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), no phases referring to the Fe species were observed, suggesting that the Fe3+ ions may be present on the surface of flower-like BiOCl. It is noted that the Fe3+ ions could lead to a morphological reconstruction from BiOCl nanosheets to BiOCl flowers. The obtained Fe/BiOCl-FCSBA-15 exhibited an excellent degradation efficiency for 2-nitrophenol, which reached nearly 100% within 40 min by optimizing parameters such as the H2O2 dosage, pH value, temperature, Fe/Bi molar ratio and Bi/Si molar ratio. The finding reported here is important and may help to develop novel mesoporous matrix based systems for advanced catalysts.
- Zhao, Qihang,Liu, Xiaoyan,Sun, Menglin,Du, Chunfang,Liu, Zhiliang
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p. 36948 - 36956
(2015/05/05)
-
- In situ decoration of plasmonic Ag nanocrystals on the surface of (BiO)2CO3 hierarchical microspheres for enhanced visible light photocatalysis
-
Novel plasmonic 0D Ag nanocrystal decorated 3D (BiO)2CO 3 hierarchical microspheres were fabricated with a one-pot hydrothermal method. The as-prepared samples were systematically characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, photoluminescence spectra, ns-level time-resolved fluorescence spectra, photocurrent generation and EIS measurement. The results indicated that the 0D Ag nanoparticles were deposited on the surface of 3D (BiO)2CO3 hierarchical microspheres. The deposited Ag nanoparticles were reduced from Ag+ by the citrate ions from bismuth citrate. The photocatalytic activity of the as-prepared samples was evaluated towards the degradation of NO at ppb-level under visible light irradiation. The intermediate NO2 was monitored on-line during the photocatalytic reaction. The pure (BiO)2CO 3 microspheres exhibited decent visible light photocatalytic activity because of the surface scattering and reflecting (SSR effect) resulting from the special 3D hierarchical architecture. The Ag-decorated (BiO) 2CO3 microspheres (Ag/BOC) exhibited greatly enhanced photocatalytic activity, photocurrent generation and promoted NO2 oxidation compared to the pure (BiO)2CO3 microspheres. The enhanced photocatalytic activity and photocurrent generation of Ag/BOC was ascribed to the cooperative contribution of the surface plasmon resonance (SPR effect), efficient separation of electron-hole pairs and prolonged lifetime of charge carriers induced by Ag nanoparticles. The photocatalytic performance of Ag/BOC was dependent on the content of Ag loading. When the amount of Ag is controlled at 5%, the highest photocatalytic performance can be achieved. Further increasing the Ag loading content promotes aggregation of the Ag particles and transforms the uniform microspheres into non-uniform microspheres, which is not beneficial to improving the activity. Importantly, the as-prepared Ag/BOC composites exhibited high photochemical stability after multiple reaction runs. The concepts of enhancing the activity through the SSR and SPR effects provide a new avenue for the development of efficient noble metal/bismuth-based plasmonic photocatalysts with attractive nano/micro architectures for efficient visible light photocatalytic activity.
- Dong, Fan,Li, Qiuyan,Zhou, Ying,Sun, Yanjun,Zhang, Haidong,Wu, Zhongbiao
-
p. 9468 - 9480
(2014/06/23)
-
- Formation and characterization of VUV photolytically-induced (NH 2)(NH3)n aggregates, 0 ≤ n ≤ 3
-
The formation of amidogen radical may be an important precursor toward the formation of prebiotic molecules on the surface of ice grains in interstellar clouds. Many laboratory experiments aimed at characterizing the photolysis of ammonia. Wide shifts wer
- Zins,Krim
-
p. 10285 - 10295
(2013/09/02)
-
- Accurate rate constants for decomposition of aqueous nitrous acid
-
Decomposition of nitrous acid in aqueous solution has been studied by stopped flow spectrophotometry to resolve discrepancies in literature values for the rate constants of the decomposition reactions. Under the conditions employed, the rate-limiting reaction step comprises the hydrolysis of NO 2. A simplified rate law based on the known elementary reaction mechanism provides an excellent fit to the experimental data. The rate constant, 1.34 × 10-6 M-1 s-1, is thought to be of higher accuracy than those in the literature as it does not depend on the rate of parallel reaction pathways or on the rate of interphase mass transfer of gaseous reaction products. The activation energy for the simplified rate law was established to be 107 kJ mol-1. Quantum chemistry calculations indicate that the majority of the large activation energy results from the endothermic nature of the equilibrium 2HNO2? NO + NO 2 + H2O. The rate constant for the reaction between nitrate ions and nitrous acid, which inhibits HNO2 decomposition, was also determined.
- Rayson, Mark S.,MacKie, John C.,Kennedy, Eric M.,Dlugogorski, Bogdan Z.
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p. 2178 - 2185
(2012/05/31)
-
- Observation of gas-phase peroxynitrous and peroxynitric acid during the photolysis of nitrate in acidified frozen solutions
-
The photolysis of nitrate embedded in ice and snow can be a significant source of volatile nitrogen oxides affecting the composition of the planetary boundary layer. In this work, we examined the nitrogen oxides evolved from irradiated frozen solutions containing nitrate. Products were monitored by cavity ring-down spectroscopy (CRDS), NO-O3 chemiluminescence (CL), and chemical ionization mass spectrometry (CIMS). Under acidic conditions, the nitrogen oxides volatilized were mainly in the form of NOz, i.e., nitrous (HONO), nitric (HONO2), peroxynitrous (HOONO), and peroxynitric acid (HO2NO2). Identification of acidic nitrogen oxides by CIMS and possible HOONO, HONO2 and HO 2NO2 formation pathways are discussed.
- Abida, Otman,Mielke, Levi H.,Osthoff, Hans D.
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p. 187 - 192
(2011/10/05)
-
- Modulation of homocysteine toxicity by S-nitrosothiol formation: A mechanistic approach
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The metabolic conversion of homocysteine (HCYSH) to homocysteine thiolactone (HTL) has been reported as the major cause of HCYSH pathogenesis. It was hypothesized that inhibition of the thiol group of HCYSH by S-nitrosation will prevent its metabolic conversion to HTL. The kinetics, reaction dynamics, and mechanism of reaction of HCYSH and nitrous acid to produce S-nitrosohomocysteine (HCYSNO) was studied in mildly to highly acidic pHs. Transnitrosation of this non-protein-forming amino acid by 5-nitrosoglutathione (GSNO) was also studied at physiological pH 7.4 in phosphate buffer. In both cases, HCYSNO formed quantitatively. Copper ions were found to play dual roles, catalyzing the rate of formation of HCYSNO as well as its rate of decomposition. In the presence of a transition-metal ions chelator, HCYSNO was very stable with a halflife of 198 h at pH 7.4. Nitrosation by nitrous acid occurred via the formation of more powerful nitrosating agents, nitrosonium cation (NO +) and dinitrogen trioxide (N2O3). In highly acidic environments, NO+ was found to be the most effective nitrosating agent with a first-order dependence on nitrous acid. N 2O3 was the most relevant nitrosating agent in a mildly acidic environment with a second-order dependence on nitrous acid. The bimolecular rate constants for the direct reactions of HCYSH and nitrous acid, N2O3, and NO+were 9.0 × 10-2, 9.50 × 103, and 6.57 × 1010 M-1 s-1, respectively. These rate constant values agreed with the electrophilic order of these nitrosating agents: HNO2 2O3 +. Transnitrosation of HCYSH by GSNO produced HCYSNO and other products including glutathione (reduced and oxidized) and homocysteineglutathione mixed disulfide. A computer modeling involving eight reactions gave a good fit to the observed formation kinetics of HCYSNO. This study has shown that it is possible to modulate homocysteine toxicity by preventing its conversion to a more toxic HTL by S-nitrosation.
- Morakinyo, Moshood K.,Strongin, Robert M.,Simoyi, Reuben H.
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p. 9894 - 9904
(2011/08/08)
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- Disproportionation pathways of aqueous hyponitrite radicals (HN 2O2/N2O2-)
-
Pulse radiolysis and flash photolysis are used to generate the hyponitrite radicals (HN2O2W2O2-) by one-electron oxidation of the hyponitrite in aqueous solution. Although the radical decay conforms to simple second-order kinetics, its mechanism is complex, comprising a short chain of NO release-consumption steps. In the first, rate-determining step, two N2O2- radicals disproportionate with the rate constant 2k = (8.2 ± 0.5) × 10 7 M-1 s-1 (at zero ionic strength) effectively in a redox reaction regenerating N2O22- and releasing two NO. This occurs either by electron transfer or, more likely, through radical recombination-dissociation. Each NO so-produced rapidly adds to another N2O2-, yielding the N3O 3- ion, which slowly decomposes at 300 s-1 to the final N2O + NO2- products. The N 2O2- radical protonates with pKa = 5.6 ± 0.3. The neutral HN2O2 radical decays by an analogous mechanism but much more rapidly with the apparent second-order rate constant 2k = (1.1 ± 0.1) × 109 M-1 s -1. The N2O2- radical shows surprisingly low reactivity toward O2 and O2-, with the corresponding rate constants below 1 × 106 and 5 × 107 M-1 s-1. The previously reported rapid dissociation of N2O2- into N2O and O- does not occur. The thermochemistry of HN2O 2/N2O2- is discussed in the context of these new kinetic and mechanistic results.
- Poskrebyshev, Gregory A.,Shafirovich, Vladimir,Lymar, Sergei V.
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p. 8295 - 8302
(2009/04/13)
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- Heterogeneous chemistry of the NO3 free radical and N 2O5 on decane flame soot at ambient temperature: Reaction products and kinetics
-
The interaction of NO3 free radical and N2O 5 with laboratory flame soot was investigated in a Knudsen flow reactor at T = 298 K equipped with beam-sampling mass spectrometry and in situ REMPI detection of NO2 and NO. Decane (C10H22) has been used as a fuel in a co-flow device for the generation of gray and black soot from a rich and a lean diffusion flame, respectively. The gas-phase reaction products of NO3 reacting with gray soot were NO, N 2O5, HONO, and HNO3 with MONO being absent on black soot. The major loss of NO3 is adsorption on gray and black soot at yields of 65 and 59%, respectively, and the main gas-phase reaction product is N2O5 owing to heterogeneous recombination of NO3 with NO2 and NO according to NO3 + {C} → NO + products. HONO was quantitatively accounted for by the interaction of NO2 with gray soot in agreement with previous work. Product N 2O5 was generated through heterogeneous recombination of NO3 with excess NO2, and the small quantity of HNO 3 was explained by heterogeneous hydrolysis of N2O 5. The reaction products of N2O5 on both types of soot were equimolar amounts of NO and NO2, which suggest the reaction N2O5 + {C} → N2O3(ads) + products with N2O3(ads) decomposing into NO + NO 2. The initial and steady-state uptake coefficients γ0 and γss of both NO3 and N 2O5 based on the geometric surface area continuously increase with decreasing concentration at a concentration threshold for both types of soot. γss of NO3 extrapolated to [NO 3] → 0 is independent of the type of soot and is 0.33 ± 0.06 whereas γss for [N2O5] → 0 is (2.7 ± 1.0) × 10-2 and (5.2 ± 0.2) × 10-2 for gray and black soot, respectively. Above the concentration threshold of both NO3 and N2O5, γss is independent of concentration with γ ss(NO3) = 5.0 × 10-2 and γss-(N2O5) = 5.0 × 10-3. The inverse concentration dependence of γ below the concentration threshold reveals a complex reaction mechanism for both NO3 and N2O5. The atmospheric significance of these results is briefly discussed.
- Karagulian, Federico,Rossi, Michel J.
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p. 1914 - 1926
(2008/10/09)
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- Carbon-containing nano-titania prepared by chemical vapor deposition and its visible-light-responsive photocatalytic activity
-
Ultraviolet and visible-light-responsive titania was synthesized and employed in the NOx photomineralization. A thermal decomposition reaction of titanium isopropoxide was carried out with a metal-organic chemical vapor deposition (MOCVD), enabling continuous production of TiO2 nanoparticles. Carbon-containing titanium dioxide with the anatase phase prepared at 500 °C under nitrogen atmosphere exhibited high photocatalytic activity for NO oxidation under visible-light illumination. Experimental results indicate that up to 48% removal of NOx can be achieved in a continuous flow type of reaction system under visible-light illumination (green LED). The chamber temperature in this MOCVD process plays an important role in lattice structure formation, and also affected TiO2 carbon content. The carbonaceous species on the TiO2 surface, shown by X-ray diffractometry (XRD), and Raman, UV-vis, and X-ray photoelectron spectroscopies (XPS), is important to the visible-light absorption and visible-light-catalytic mineralization of NOx.
- Kuo, Chien-Sheng,Tseng, Yao-Hsuan,Huang, Chia-Hung,Li, Yuan-Yao
-
-
- Generation of nitric oxide by photolysis of silver hyponitrite in suspension induced by LMCT excitation
-
The yellow colour of silver hyponitrite is attributed to an LMCT band at λmax = 419 nm. Solid Ag2N2O2 and its suspensions in water or acetonitrile are light sensitive. LMCT excitation leads to a photolysis according to the equation Ag2N2O2 → 2Ag + 2NO. In the presence of air and water, NO is finally converted to HNO2.
- Kunkely, Horst,Vogler, Arnd
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p. 1294 - 1296
(2008/10/09)
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- Reduction of NO2 to nitrous acid on illuminated titanium dioxide aerosol surfaces: Implications for photocatalysis and atmospheric chemistry
-
TiO2, a component of atmospheric mineral aerosol, catalyses the reduction of NO2 to nitrous acid (HONO) when present as an aerosol and illuminated with near UV light under conditions pertinent to the troposphere. The Royal Society of Chemistry 2006.
- Gustafsson, R. Joel,Orlov, Alexander,Griffiths, Paul T.,Cox, R. Anthony,Lambert, Richard M.
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p. 3936 - 3938
(2007/10/03)
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- Iron and manganese corroles are potent catalysts for the decomposition of peroxynitrite
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Ring cycle: Iron and manganese corroles are among the most efficient decomposition catalysts of peroxynitrite reported to date. The catalytic rate of the iron complex is higher than that of analogous porphyrins, and the manganese complex operates through
- Mahammed, Atif,Gross, Zeev
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p. 6544 - 6547
(2007/10/03)
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- The state of ruthenium in nitrite-nitrate nitric acid solutions as probed by NMR
-
The state of ruthenium in nitric acid solutions treated with sodium nitrite has been studied by 14N, 15N, 17O, and 99Ru NMR. In the acidity range 2.7-0.12 mol/L, the dominating ruthenium species are the [RuNO(NO
- Emel'yanov,Fedotov
-
p. 1811 - 1819
(2008/10/09)
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- Oxidation of U(IV) in HNO3 solutions containing urea and Tc(VII)
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The kinetics of U(IV) oxidation with nitric acid in aqueous solutions containing urea, catalyzed with technetium ions, were studied by sampling with subsequent colorimetric determination of the U(IV) concentration. At the constant ionic strength of the solution μ = 2 in the range of the initial concentrations of U(IV) from 2 × 10-3 to 1.28 × 10 -2, Tc(VII) from 5 × 10-5 to 1 × 10 -3, urea from 0.01 to 0.1, and hydrogen ions from 0.4 to 1.96 M, the reaction rate is described by the equation -d[U(IV)]/dt = k 1[U(IV)] [Tc]0.5[CO(NH2)2] × {[H+] 2 + β1[H+] + β2} -1 - k 2[U(IV)]2[H+] 0.4[CO(NH2)2]1.6{ [H +]2 + β1[H+]+ β2}-2, where k 1 = 172 ± 10 mol0.5 l-0.5 min-1 and k 2 = (9.4±1.2)×102 mol l-1 min-1 at 25°C, β1 and β2 are the hydrolysis constants of U4+ ions. The activation energy is 63±2 kJ mol -1. A reaction mechanism is proposed, in which in the slow stages the complex ion U(OH) 2 2+ ?CO(NH2) 2 reacts with TcO2+ and TcO2+ ? CO(NH 2)2 ions. 2005 Pleiades Publishing, Inc.
- Dvoeglazov,Marchenko,Koltunov
-
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- Formation of nitric acid in the gas-phase HO2 + NO reaction: Effects of temperature and water vapor
-
A high-pressure turbulent flow reactor coupled with a chemical ionization mass spectrometer was used to investigate the minor channel (Ib) producing nitric acid, HNO3, in the HO2 + NO reaction for which only one channel (la) is known so far: HO2 + NO → OH + NO 2 (la), HO2 + NO → HNO3 (1b). The reaction has been investigated in the temperature range 223-298 K at a pressure of 200 Torr of N2 carrier gas. The influence of water vapor has been studied at 298 K. The branching ratio, k1blk1a, was found to increase from (0.18+-0.06+0.04)% at 298 K to (0-87 -0.08+0.05)% at 223 K- corresponding to k1b = (1.6 ±0.5) x 10-14 and (10.4 ±1.7) ×10 -14 cm3 molecule -1 s-l, respectively at 298 and 223 K. The data could be fitted by the Arrhenius expression k1b = 6.4 × 10-17 exp((1644 ±76)l7) cm 3 molecule-1 s-1 at T = 223-298 K. The yield of HNO3 was found to increase in the presence of water vapor (by 90% at about 3 Torr of H2O). Implications of the obtained results for atmospheric radicals chemistry and chemical amplifiers used to measure peroxy radicals are discussed. The results show in particular that reaction Ib can be a significant loss process for the HOx (OH, HO2) radicals in the upper troposphere.
- Butkovskaya,Kukui,Pouvesle,Le Bras
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p. 6509 - 6520
(2008/10/09)
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- Heterogeneous reaction of nitric acid with nitric oxide on glass surfaces under simulated atmospheric conditions
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The heterogeneous reaction of nitric acid (HNO3) with nitric oxide (NO) on borosilicate glass surfaces was studied in a flow system at relative humidity levels in the range 21-86%. Reactant concentrations were kept closer to ambient atmospheric levels as compared to all previous studies of this reaction. Within experimental error, no formation of the proposed reaction products nitrous acid (HONO) and nitrogen dioxide (NO2) was observed. Upper limits of the reactive uptake coefficients of NO on borosilicate glass surfaces, covered with ～1 monolayer of HNO3, were determined: γ(NO→HONO) -11 and γ(NO→NO2) -9. These values are significantly lower than previously reported values, which were determined at higher reactant concentrations. Results obtained upon investigation of the secondary heterogeneous reaction of the proposed product HONO with HNO 3 under identical experimental conditions show that HONO should be observed in the study of the reaction HNO3 + NO, if it is formed. Thus, the obtained upper limit γ(NO→HONO) is representative for the reaction HNO3 + NO → HONO + NO2. Under the assumption that the glass surfaces, typically used in laboratory studies of this reaction, are representative for environmental surfaces, the latter reaction is unimportant for atmospheric HONO formation and for a renoxification of the atmosphere.
- Kleffmann, Joerg,Benter, Thorsten,Wiesen, Peter
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p. 5793 - 5799
(2007/10/03)
-
- Photofragment translational spectroscopy of nitric acid at 248 nm with VUV photoionization detection of products
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This study examines the 248-nm photodissociation of nitric acid (HNO 3) and characterizes the translational energy distribution of the nascent photofragments. Photofragment translational spectroscopy with VUV photoionization detection evidenced one product channel, cleavage of HNO 3 to form OH + NO2, and established an upper limit on the contribution from the O + HONO formation channel of 3%. These data contribute an independent measurement to a literature debate regarding the branching between these two channels.
- Krisch,Reid,McCunn,Butler,Shu
-
-
- Autocatalytic Nitration of Pyrene by Aerated Nitrogen Dioxide in Solution and Comparison with the Nitration on Silica Particles
-
The nitration mechanism of pyrene (PYH) by aerating NO2 in solution was studied by varying the factors (concentration of NO2, addition of HNO3 gas and H2O, 1-substituent on PYH, and solvent) affecting the nitration. Only 1-nitropyrene was formed, In acetonitrile, both the decrease in PYH and the increase in 1-nitropyrene depicted sigmoid curves, that is, their changes proceeded abruptly after an induction period, and finally approached to zero, The characteristic feature was reasonably explained by the facts that H+ dissociated from HNO3, accumulated by aerating NO2 into trace water-containing acetonitrile and released by the nitration, acted as an autocatalyst. The nitration proceeded electrophilically based on the 1-substituent effect of PYH, and accelerated with increasing polarity of the solvents. The nitration was studied kinetically and an ionic mechanism involving NO2+ as an electrophile was proposed. The nitration mechanism of PYH in acetonitrile was different from that in the adsorbed water on silica gel.
- Hasegawa, Kiyoshi,Kaneko, Hiroshi,Ogawa, Tatsuya
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p. 147 - 155
(2007/10/03)
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- Direct determination of the Gibbs' energy of formation of peroxynitrous acid
-
The kinetics of decomposition of peroxynitrous acid (ONOOH) was investigated in the presence of 0.1-0.75 M HClO4 and at a constant ionic strength. The decay rate of ONOOH decreased in the presence of H2O2, approaching a limiting value well below 75 mM H2O2. It also decreased in the presence of relatively low [HNO2] but did not approach a lower limiting value, since ONOOH reacts directly with HNO2. The latter reaction corresponds to a HNO2- and H+-catalyzed isomerization of ONOOH to nitrate, and its third-order rate constant was determined to be 520 ± 30 M-2 s-1. The mechanism of formation of O2NOOH from ONOOH in the presence of H202 was also scrutinized. The results demonstrated that in the presence of 0.1-0.75 M HClO4 and 75 mM H2O2 the formation of O2NOOH is insignificant. The most important finding in this work is the reversibility of the reaction ONOOH + H2O ? HNO2 + H2O2 and its equilibrium constant was determined to be (7.5 ± 0.4) × 10-4 M. Using this value, the Gibbs' energy of formation of ONOOH was calculated to be 7.1 + ± 0.2 kcal/mol. This figure is in good agreement with the value determined previously from kinetic data using parameters for radicals formed during homolysis of peroxynitrite.
- Merenyl, Gabor,Lind, Johan,Czapski, Gideon,Goldstein, Sara
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p. 3796 - 3800
(2008/10/08)
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- Product analysis of selective catalytic reduction of NO2 with C2H4 over H-ferrierite
-
The reaction paths for the selective reduction of NO2 with C2H4 over H-ferrierite were studied by focusing on the formation and reaction of the by-products. Nitroethylene (NE), HCN, and HNCO were detected as nitrogen-containing by-products in C2H4-SCR-NO2. NE was converted to HNCO, HCN, NH3, HCHO, CO, and CO2 in the absence of NOx. HNCO had a high reactivity for hydrolysis and was fully decomposed into NH3 and CO2 above 200°C. HNCO hydrolysis followed by the reaction of NH3 with NOx to form N2 was a very feasible pathway. HCN was mostly hydrolyzed to NH3 and CO at high temperatures and partly oxidized to HNCO in the presence of NO2. N2 and N2O were formed by the reactions of NH3 with NO, and NH3 with NO2. The latter reaction was much faster. Two reaction pathways were observed for N2 formation, i.e. the direct reaction between NE and NO2, and NE decomposition followed by the formation and hydrolysis of HNCO. The second pathway resulted in the formation of NH3, which further reacted with NOx to form N2.
- Nanba,Obuchi,Sugiura,Kouno,Uchisawa,Kushiyama
-
-
- Infrared spectra and molecular dynamics simulations of cis-HONO isomer in an argon matrix
-
Temperature dependent infrared spectra of cis-HONO trapped in an argon matrix are presented. All observed cis-HONO fundamental bands appear as doublets in the spectra. Both components of each doublet show reversible temperature broadening. Molecular dynamics simulations of cis-HONO trapping in an argon matrix suggest that the molecule is trapped in a one-atom substitutional cage in solid argon; no evidence of non-equivalent trapping sites was found. Experimental and theoretical results are discussed.
- Talik, Tadeusz,Tokhadze, Konstantin G.,Mielke, Zofia
-
-
- H+NO2 channels in the photodissociation of HONO at 193.3 nm
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The H+NO2 channels in the 193.3-nm photodissociation of jet-cooled HONO have been examined by using high-n Rydberg-atom time-of-flight (HRTOF) technique. Center-of-mass (CM) translational energy distribution and energy-dependent angular distribution of the photoproducts reveal that the NO2 fragments are produced in at least three electronic states: ground X2A1 and excited qq2B2 and qq2B1 (and/or C2A2) states. The overall average CM product translational energy is 〈ET〉 = 0.3Eavail. NO2 fragments are highly vibrationally excited in each of these electronic states, and in particular, a long vibrational progression of NO2 bending mode in the qq2B2 state has been observed. Branching ratios of the NO2 electronic states are estimated: X2A1:qq2B2: qq2B1/C2A2≈0.13:0.21:0.66. The O-H bond photodissociation of HONO from the second electronically excited singlet state B1A′ proceeds via multiple dissociation pathways. The H+NO2(qq2B2) product channel is via a direct dissociation (presumably in a near-planar fragmentation geometry) and has a large translational energy release, a specific NO2 bending vibration population (indicating a significant change of the ONO angle during dissociation), and an anisotropic product angular distribution (suggesting a short excited qq1A′ state lifetime with respect to dissociation). The H+NO2(X2A1) channel could be produced from a triplet excited state (which likely has a repulsive barrier along the O-H dissociation coordinate) following intersystem crossing or from the ground state of HONO after internal conversion. The H+NO2(qq2B1) channel requires nonadiabatic processes in a planar geometry, while in nonplanar geometries, it can be directly produced from the HONO(qq1A′) state, consistent with its large branching ratio.
- Amaral,Xu,Zhang
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p. 1465 - 1475
(2007/10/03)
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- NMR study of reactions between Pd, Ru, and Rh nitrite complexes with sulfamic acid
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Reactions of nitrite complexes of Pd, Ru, and Rh with sulfamic acid were studied by the 14, 15N, and 17O NMR method. Chemical shifts were assigned, and the predominant forms of the complexes were established. The reaction products at room temperature are cis-nitroaqua complexes. Coordination of the sulfamate ion upon storage for a long time or on heating was detected.
- Belyaev,Emel'yanov,Khranenko,Fedotov
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p. 184 - 194
(2008/10/08)
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- Enhancement of N2O4 on Porous Glass at Room Temperature: A Key Intermediate in the Heterogeneous Hydrolysis of NO2?
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The heterogeneous hydrolysis of NO2 at surfaces in the atmosphere is believed to be a significant source of HONO, a key OH precursor in urban areas. However, the mechanism of this reaction is not known. The uptake of 2.9 Torr of NO2 in N2 at a total pressure of 508 Torr on a porous glass surface with varying amounts of surface-adsorbed water was studied using FTIR at 294 K. The ratio of N2O4 to NO2 was enhanced on the glass surface relative to the gas phase. On a relatively dry surface, the formation of surface-adsorbed HNO3 was observed over a period of ca. 20 h, likely due to the reaction with small amounts of water on the surface. Gas-phase NO and N2O were also generated. When larger amounts of water were initially present on the surface, surface-adsorbed HNO3 was formed immediately, as well as gas-phase NO, N2O, and HONO. Although the NO2 concentrations used in the present studies are much larger than those found in the atmosphere, this work suggests that N2O4 should be considered as a key intermediate in the heterogeneous hydrolysis of NO2 to form HONO.
- Barney, W. S.,Finlayson-Pitts, B. J.
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p. 171 - 175
(2007/10/03)
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- Rate coefficients for the OH + CF3I reaction between 271 and 370 K
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The rate coefficient, k1, for the reaction OH + CF3I → products was measured under pseudo-first-order conditions in hydroxyl radical, OH. OH temporal profiles were monitored by laser-induced fluorescence (LIF), and CF3I concentrations were determined by UV/Visible absorption. We determined k1 (T) to be (2.10 ± 0.80) × 10-11 exp[-(2000 ± 140)/T] cm3 molecule-1 s-1, over the temperature range 271 to 370 K. The quoted uncertainties are 2σ (95% confidence limits, σA = AσlnA). Previous measurements of k1(T) are compared with our values, and possible reasons for the discrepancies are discussed. The heat of formation of HOI is deduced to be less than -16 kcal mole-1, if the products of reaction 1 are mostly HOI and CF3. These measurements support the earlier conclusion that the reaction of OH with CF3I plays a negligibly small role in the atmospheric removal of CF3I.
- Gilles, Mary K.,Talukdar,Ravishankara
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p. 8945 - 8950
(2007/10/03)
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- A unique method for laboratory quantification of gaseous nitrous acid (HONO) using the reaction HONO + HCL → ClNO + H2O
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A novel method for quantifying gaseous HONO in laboratory systems has been developed. The technique uses the reaction of gas phase HONO with an excess of HCl gas to yield nitrosyl chloride (ClNO), which was quantified using FTIR. The gas-phase reaction of HONO with HCl formed ClNO with a stoichiometry of 0.9 ± 0.2 (1σ), i.e., within experimental error of unity. The concentration-time profiles for HONO and ClNO were fitted with a kinetics model, which showed that the reaction HONO + HCl → ClNO + ClNO was slow (k1 ≤ (1.9 ± 1.3) x 10-19/mole-sec (2σ) at 297 K. However, the reaction was a useful approach for quantifying HONO in laboratory systems because calibration for ClNO can be readily made. The method is better than UV/visible spectroscopy in that it does away with the more complex data associated with DOAS and other species (e.g., HNO3), which cannot be measured by DOAS, can be determined. Compared to the denuder and NOx detector approaches, the method is also more direct and specific.
- Wingen, Lisa M.,Barney, William S.,Lakin, Matthew J.,Brauers, Theo,Finlayson-Pitts, Barbara J.
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p. 329 - 335
(2007/10/03)
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- Nitric/Nitrous Acid Equilibria in Supercritical Water
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UV - vis spectroscopy was utilized to measure the decomposition of aqueous HNO3 solutions above 300 °C, in some cases with added NaOH, H2O2, and/or NaNO2, to form NO2, HNO2, NO, N2/su
- Chlistunoff, Jerzy,Ziegler, Kirk J.,Lasdon, Leon,Johnston, Keith P.
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p. 1678 - 1688
(2007/10/03)
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