3352-57-6Relevant articles and documents
Diffusion-Kinetic Modeling of the Electron Raiolysis of Water at Elevated Temperatures
LaVerne, Jay A.,Pimblott, Simon M.
, p. 3291 - 3297 (1993)
The temperature dependence of the chemistry in the track of a fast electron in water has been examined with a deterministic diffusion-kinetic model.The model calculations suggest that there is an increase in the yields of the hydrated electron and hydroxyl radical and a decrease in the yields of molecular hydrogen and hydrogen peroxide with increasing temperature.These results are consistent with most of the experimental data.It is found that the best fit to the experimental data occurs when the radius of the initial spatial distribution of the hydrated electron is dependent on a process which scales according to an Arrhenius-like equation with an activation energy similar to that for electron movement between potential traps in water.The radii of the initial spatial distributions of all the other species appear to be independent of the temperature.The predictions of the model suggest that the initial radiation chemical yields of the reactive species are independent of temperature.An additional thermally dependent reaction for the decomposition of water is not required for the model predictions to match the experimental data.
Experimental Determination of the OH Product Yield from NH2 + NO at 300 K
Dolson, David A.
, p. 6714 - 6718 (1986)
The branching ratio, α = k1b/k1a, has been experimentally determined at 300 K for two product channels of the NH2 + NO reaction: -->N2 + H2O (k1a) and --> N2H + OH (k1b).The reaction was studied in a fast-flow tube reactor coupled to a modulated-beam mass spectrometer.CO was added to scavenge hydroxyl radicals via OH + CO --> CO2 + H.Separate experiments and kinetic modeling results confirm that the scavenging efficiency is near unity so that is a good measure of .The branching ratio, α = / = /, was determined from CO2+ and H2O+ ion intensities to be 0.15 at 300 K.This result is discussed as it relates to previous measurements and to the atmospheric chemistry of ammonia.
A Flash Photolysis-Shock Tube Kinetic Study of the H Atom Reaction with O2: H+O2=OH+O (962 KHO2+Ar (746 K
Pirraglia, A. N.,Michael, J. V.,Sutherland, J. W.,Klemm, R. B.
, p. 282 - 291 (1989)
Rate constants for the reactions H+O2->OH+O (1) and H+O2+M->HO2+M (2) were measured under pseudo-first-order conditions by the flash photolysis-shock tube technique that employs the atomic resonance absorption detection method to monitor t.Rate data for reaction 1 were obtained over the temperature range from 962 to 1705 K, and the results are well represented by the Arrhenius expression k1(T)=(2.79+/-0.32)*10-10 exp(-16132+/-276 cal mol-1/RT) cm3 molecule-1 s-1.The mean deviation of the experimentally measured rate constants from those calculated by using this expression is +/-16percent over the stated temperature range.The recent shock tube data of Frank and Just (1693-2577 K) were combined with the present results for k1(T) to obtain the following Arrhenius expression for the overall temperature span (962-2577 K): k1(T)=(3.18+/-0.24)*10-10 exp(-16439+/-186 cal mol-1/RT) cm3 molecule-1 s-1.The mean deviation of the experimentally measured rate constants from this expression is +/-15percent over the entire temperature range.Values for the rate constant for the reverse of reaction 1 were calculated from each of the experimentelly measured k1(T) values with expressions for the equilibrium constant derived by using the least JANAF thermochemical data.These k-1(T) values were also combined with similarly derived values from the Frank and Just data.This combined data base showed that k-1(T) was essentially constant between 962 and 2577 K with an average value of 2.05*10-11 cm3 molecule-1 s-1 and a one standard deviation uncertainty of 0.42*10-11 cm3 molecule-1 s-1.Kinetic results were also derived for reaction 2 from the difference between the experimental first-order t decays and the corresponding calculated k1(T) values.The temperature span over which k2 data could be determined was limited 746 Ka slight negative temperature dependence, the magnitude of the uncertainties in the k2 results and the limited temperature span that could be covered preclude the calculation of reliable Arrhenius parameters.Instead, a simple average value may be used to represent this rate constant, k2=(7.1+/-1.9)*10-33 cm6 molecule-2 s-1, where the error limit is given at the one standard deviation level.All the results obtained are compared with those of previous investigations.
A Study of the Reaction Li + O2 + M (M = N2, He) over the Temperature Range 267-1100 K by Time-Resolved Laser-Induced Fluorescence of Li(22PJ-22S1/2)
Plane, John M. C.,Rajasekhar, B.
, p. 3884 - 3890 (1988)
We present an investigation of the recombination reaction between lithium atoms and O2 in the presence of both N2 and He as bath gases.Lithium atoms were produced by the pulsed photolysis of either LiI, LiOH, or LiO2 molecules in the presence of an excess of O2 and the bath gas.The Li atom concentration was then monitored by laser-induced fluorescence of the metal atoms at λ = 670.7 nm using a pulsed nitrogen-pumped dye laser and boxcar integration of the fluorescence signal.Termolecular behavior was demontstrated in the case of both bath gases, and absolute third-order rate constants were obtained over the temperature range 267-1100 K.A fit of these data to the form AT-n yields k(M = N2) = (4.30 +/- 1.36) * 10-30(T/300 K)-(1.02 +/- 0.06) cm6 molecule-2 s-1 and k(M = He) = (1.25 +/- 0.48) * 10-30(T/300 K)-(0.38 +/- 0.08) cm6 molecule-2 s-1.It is demontstrated that these measurements are essentially in the low-pressure limit; the rate coefficients are then extrapolated from the experimental temperature range to ambient mesospheric temperatures ( 140 K a satisfactory fit to the Troe formalism.
Decay dynamics of H2O(A1B1) excitation by two photon absorption at 354.6 nm
Mikulecky,Gericke,Comes
, p. 927 - 929 (1991)
Water was photolyzed at 177.3 nm via a two-photon excitation by a frequency-tripled Nd:YAG laser (354.6 nm). The complete product state distribution of the ejected OH product was determined by LIF. The OH is produced in the vibrational ground state exclusively. OH shows a Boltzmann-type rotational distribution with a temperature parameter of about 350 K. No preferred population of A- or spin-orbit states was observed.
Role of Hydrogen Bonding by Thiones in Protecting Biomolecules from Copper(I)-Mediated Oxidative Damage
Rai, Rakesh Kumar,Chalana, Ashish,Karri, Ramesh,Das, Ranajit,Kumar, Binayak,Roy, Gouriprasanna
, p. 6628 - 6638 (2019)
The sulfur-containing antioxidant molecule ergothioneine with an ability to protect metalloenzymes from reactive oxygen species (ROS) has attracted significant interest in both chemistry and biology. Herein, we demonstrated the importance of hydrogen bonding in S-oxygenation reactions between various thiones and H2O2 and its significance in protecting the metal ion from H2O2-mediated oxidation. Among all imidazole- and benzimidazole-based thiones (1-10), ImMeSH (2) showed the highest reactivity toward H2O2 - almost 10 and 75 times more reactive than N,N′-disubstituted ImMeSMe (5) and BzMeSMe (10), respectively. Moreover, metal-bound ImMeSH (2) of [TpmCu(2)]+ (13) was found to be 51 and 1571 times more reactive toward H2O2 than the metal-bound ImMeSMe (5) of [TpmCu(5)]+ (16), and BzMeSMe (10) of [TpmCu(10)]+ (21), respectively. The electron-donating N-Me substituent and the free N-H group at the imidazole ring played a very crucial role in the high reactivity of ImMeSH toward H2O2. The initial adduct formation between ImMeSH and H2O2 (ImMeSH·H2O2) was highly facilitated (-23.28 kcal mol-1) due to the presence of a free N-H group, which leads to its faster oxygenation than N,N′-disubstituted ImMeSMe (5) or BzMeSMe (10). As a result, ImMeSH (2) showed a promising effect in protecting the metal ion from H2O2-mediated oxidation. It protected biomolecules from Cu(I)-mediated oxidative damage of through coordination to the Cu(I) center of [TpmCu(CH3CN)]+ (11), whereas metal-bound ImMeSMe or BzMeSMe failed to protect biomolecules under identical reaction conditions.
Formation of hydroxyl radical from the photolysis of frozen hydrogen peroxide
Chu, Liang,Anastasio, Cort
, p. 6264 - 6271 (2005)
Hydrogen peroxide (HOOH) in ice and snow is an important chemical tracer for the oxidative capacities of past atmospheres. However, photolysis in ice and snow will destroy HOOH and form the hydroxyl radical (·OH), which can react with snowpack trace species. Reactions of ·OH in snow and ice will affect the composition of both the overlying atmosphere (e.g., by the release of volatile species such as formaldehyde to the boundary layer) and the snow and ice (e.g., by the ·OH-mediated destruction of trace organics). To help understand these impacts, we have measured the quantum yield of ·OH from the photolysis of HOOH on ice. Our measured quantum yields (Φ(HOOH → ·OH)) are independent of ionic strength, pH, and wavelength, but are dependent upon temperature. This temperature dependence for both solution and ice data is best described by the relationship ln(Φ(HOOH → ·OH)) = -(684 ± 17)(1/T) + (2.27 ± 0.064) (where errors represent 1 standard error). The corresponding activation energy (Ea) for HOOH (5.7 kJ mol-1) is much smaller than that for nitrate photolysis, indicating that the photochemistry of HOOH is less affected by changes in temperature. Using our measured quantum yields, we calculate that the photolytic lifetimes of HOOH in surface snow grains under midday, summer solstice sunlight are approximately 140 h at representative sites on the Greenland and Antarctic ice sheets. In addition, our calculations reveal that the majority of ·OH radicals formed on polar snow grains are from HOOH photolysis, while nitrate photolysis is only a minor contributor. Similarly, HOOH appears to be much more important than nitrate as a photochemical source of ·OH on cirrus ice clouds, where reactions of the photochemically formed hydroxyl radical could lead to the release of oxygenated volatile organic compounds to the upper troposphere.
The reaction of anthracene with OH radicals: An experimental study of the kinetics between 58 and 470 K
Goulay,Rebrion-Rowe,Le Garrec,Le Picard,Canosa,Rowe
, (2005)
The first direct measurement of the reaction rate constant of a polycyclic aromatic hydrocarbon in the gas phase in the temperature range 58-470 K is reported. The reaction is OH+ anthracene and the experiment has been performed in a continuous flow Cintique de Raction en Ecoulement Supersonique Uniforme apparatus, which had to be modified for this purpose. Pulsed laser photolysis of H2 O2 has been used to generate OH radicals and laser-induced fluorescence to observe the kinetic decay of the radicals and hence determine the rate coefficients. The reaction is found to be fast, and the rate constant increases monotonically as the temperature is lowered. The rate coefficients match the expression k (cm3 molecules-1 s-1) =1.12× 10-10 (T300) -0.46.
Measurements of ground-state OH rotational energy-transfer rates
Kliner, Dahv A.V.,Farrow, Roger L.
, p. 412 - 422 (1999)
We have studied rotational energy transfer (RET) in collisions of OH with the bath gases Ar, N2, O2, and H2O at 293 K. Rotationally hot OH(X2Π3/2,v″=0,N ″=1-12) was generated by photolysis of H2O2 at 266 nm, and collisional relaxation of the nascent rotational distribution was monitored by laser-induced fluorescence. The data are remarkably well described by an exponential-gap model for the matrix of state-to-state RET rate constants. For Ar, N2, and O2, RET rates are significantly faster at low N″ than high N″; for H2O, RET is approximately an order of magnitude faster than for the other bath gases, and the rate is not as strongly dependent on N″. The rates of rotationally inelastic energy transfer are similar in the X and A states, but the X-state depopulation rate constants (including nearly elastic, Λ-doublet-changing collisions) are faster than the A-state values. By comparing the depopulation rates derived from the present experiment with previous linewidth measurements, we conclude that RET is the dominant source of pressure broadening for OH microwave transitions and makes a significant contribution for ultraviolet A-X transitions. While generally good agreement is found between the present results and previous OH RET studies for both the ground and excited electronic states, some significant discrepancies are noted.
The nascent OH detection in photodissociation of 2-(bromomethyl)hexafluoro- 2-propanol at 193 nm: Laser-induced fluorescence study
Indulkar, Yogesh N.,Upadhyaya, Hari P.,Kumar, Awadhesh,Waghmode, Suresh B.,Naik, Prakash D.
, p. 210 - 219 (2011)
Photodissociation of 2-(bromomethyl)hexafluoro-2-propanol (BMHFP) and 3-bromo-1-propanol (BP), involving σC-BrnBr transition at 193 nm, has been investigated by measuring laser-induced fluorescence spectra of the expected OH product. The OH channel is a minor dissociation pathway with a quantum yield of 0.17 ± 0.05 in BMHFP, whereas it was not observed in BP. Partitioning of the available energy into translation, rotation, and vibration of the photoproducts has been measured by state selective detection of the nascent OH product in BMHFP. OH is produced mostly in the ground vibrational level (v″ = 0), with a rotational distribution being characterized by a temperature of 465 ± 25 K. But, a significant fraction of the available energy of 30.2 kcal mol-1 is partitioned into translation of OH (14.6 kcal mol-1). The OH(v″ = 0, J″) populations in the spin-orbit states as well as in the Λ-doublet states are statistical. A plausible mechanism of OH formation on excitation of BMHFP at 193 nm is suggested, with the primary reaction channel being elimination of Br atom by direct C-Br bond dissociation from a repulsive surface. The Br radical is detected using (2 + 1) resonance-enhanced multiphoton ionization (REMPI) at ～234 nm. It is produced in both the ground (2P3/2) and the excited (2P1/2) spin-orbit states with the relative quantum yield of the latter to be 0.36. The co-fragment of Br undergoes secondary C-O bond dissociation to produce OH and F3C-C(CH 2)-CF3, with the reaction having a barrier located in the exit channel. In this two-step three-body dissociation process, a major fraction of the available energy is released into translation (〈fT〉 ～ 0.75), resulting from an impulsive C-Br bond dissociation in the primary step and presence of an exit barrier in the secondary process. Experimental results combined with theoretical calculations provide a clear picture of the dynamics of OH formation from BMHFP at 193 nm. In addition, the energetics of another channel, competing with OH, have been calculated from the primary product F3C-C(CH2)(OH)-CF3. In contrast to BMHFP, the OH product could not be observed from the photolysis of 3-bromo-1-propanol (another saturated halogenated propanol) at 193 nm under the detection limit of the present experimental condition, although it has a higher absorption cross-section at 193 nm.
