Vibrational excitation of H2O and HOD molecules produced by reactions of OH and OD with cyclo-C6H12, n-C4H10, neo-C5H12, HCI, DCI and NH3 as studied by infrared chemiluminescence

Butkovskaya,Setser

, p. 2434 - 2447 (1998)

The room-temperature reactions of OH(OD) radicals with cyclo-C6H12,n-C4H10, and neo-C5H12 have been investigated by observing the infrared chemiluminescence from the H2O(HOD) molecules generated in a fast-flow reactor. These hydrocarbon molecules are representative for abstraction from secondary and primary C-H bonds. The total vibrational energy released to H2O(HOD) was in the range of (fv)=0.55-0.65. The majority (80%-85%) of the vibrational energy is in the stretching modes and the main energy release is to the local mode associated with the new OH bond. The dynamics associated with the energy disposal to H2O(HOD) resemble the H+L-H dynamics for the analogous reactions of F atoms. The data from H2O and HOD are complementary because of the different collisional coupling between the energy levels of the v1. v2. and v modes: however, no specific isotope effect was found for the energy disposal to H2O versus HOD for reactions with the hydrocarbon molecules. In contrast, a very unusual isotope effect was found between the OH+HCl and OD+ HCl pairs The latter reaction gave the expected stretching mode excitation of HOD: however, the OH reaction gave H2O molecules with virtually no vibraitonal energy. This anomalous situation is partly associated with an inverse secondary kinetic-isotope effect, but the main isotope effect is on the dynamics of the energy disposal process itetf.

Small, P. A.

, p. 820 - 823 (1937)

Reaction pathways and site requirements for the activation and chemical conversion of methane on Ru-based catalysts

Wei, Junmei,Iglesia, Enrique

, p. 7253 - 7262 (2004)

Kinetic and isotopic tracer and exchange measurements were used to determine the identity and reversibility of elementary steps required for CH4 reforming reactions on Ru-based catalyst. CH4 reactions were limited by C-H bond activat

Topley, B.,Eyring, H.

, p. 217 - 220 (1934)

Requirements for functional models of the iron hydrogenase active site: D2/H2O exchange activity in {(μ-SMe)(μ-pdt)[Fe(CO)2(PMe3)] 2+}[BF4-]

Georgakaki, Irene P.,Miller, Matthew L.,Darensbourg, Marcetta Y.

, p. 2489 - 2494 (2003)

Hydrogen uptake in hydrogenase enzymes can be assayed by H/D exchange reactivity in H2/D2O or H2/D2/H2O mixtures. Diiron(I) complexes that serve as structural models for the active site of iron hydrogenase are not active in such isotope scrambling but serve as precursors to FeIIFeII complexes that are functional models of [Fe]H2ase. Using the same experimental protocol as used previously for {(μ-H)(μ-pdt)[Fe(CO)2(PMe3)] 2+}, 1-H+ (Zhao et al. J. Am. Chem. Soc. 2001, 123, 9710), we now report the results of studies of {(μ-SMe)(μ-pdt)[Fe(CO)2(PMe3)]2 +}, 1-SMe+, toward H/D exchange. The 1-SMe+ complex can take up H2 and catalyze the H/D exchange reaction in D2/H2O mixtures under photolytic, CO-loss conditions. Unlike 1-H+, it does not catalyze H2/D2 scrambling under anhydrous conditions. The molecular structure of 1-SMe+ involves an elongated Fe...Fe separation, 3.11 A, relative to 2.58 A in 1-H+. It is proposed that the strong SMe- bridging ligand results in catalytic activity localized on a single FeII center, a scenario that is also a prominent possibility for the enzyme active site. The single requirement is an open site on FeII available for binding of D2 (or H2), followed by deprotonation by the external base H2O (or D2O).

Farkas, L.,Farkas, A.

, p. 1071 - 1079 (1934)

Isotope effects in liquid water by infrared spectroscopy

Max, Jean-Joseph,Chapados, Camille

, p. 4626 - 4642 (2002)

The heavy and light liquid water (H2O-D2O) mixtures were studied by Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. The deformation bands of liquid water clearly indicate the presence of the three typ

Micropolarity and Hydrogen-Bond Donor Ability of Environmentally Friendly Anionic Reverse Micelles Explored by UV/Vis Absorption of a Molecular Probe and FTIR Spectroscopy

Girardi, Valeria R.,Silber, Juana J.,Falcone, Ruben Darío,Correa, N. Mariano

, p. 759 - 765 (2018)

In the present work we show how two biocompatible solvents, methyl laurate (ML) and isopropyl myristate (IPM), can be used as a less toxic alternative to replace the nonpolar component in a sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT) reverse micelles (RMs) formulation. In this sense, the micropolarity and the hydrogen-bond ability of the interface were monitored through the use of the solvatochromism of a molecular probe (1-methyl-8-oxyquinolinium betaine, QB) and Fourier transform infrared spectroscopy (FTIR). Our results demonstrate that the micropolarity sensed by QB in ML RMs is lower than in IPM RMs. Additionally, the water molecules form stronger H-bond interactions with the polar head of AOT in ML than in IPM. By FTIR was revealed that more water molecules interact with the interface in ML/AOT RMs. On the other hand, for AOT RMs generated in IPM, the weaker water–surfactant interaction allows the water molecules to establish hydrogen bonds with each other trending to bulk water more easily than in ML RMs, a consequence of the dissimilar penetration of nonpolar solvents into the interfacial region. The penetration process is strongly controlled by the polarity and viscosity of the external solvents. All of these results allow us to characterize these biocompatible systems, providing information about interfacial properties and how they can be altered by changing the external solvent. The ability of the nontoxic solvent to penetrate or not into the AOT interface produces a new interface with attractive properties.

Temperature programmed desorption studies of OD coadsorbed with H2 on Pt(111)

Backstrand, Kyle M.,Weibel, Michael A.,Moision, Robert M.,Curtiss, Thomas J.

, p. 7209 - 7218 (2000)

A molecular beam source of pure hydroxyl radicals has been developed and used to explore the water reaction catalyzed over Pt(111). An electrostatic hexapole selectively focused OD radicals from a supersonic corona discharge source onto a Pt target at a surface temperature of TS=143 K. Subsequent D2O temperature programmed desorption (TPD) spectra revealed two major features, one near TS ca. 170 K from desorption of molecular water overlayer and a second near TS ca. 210 K from the decomposition of an adsorbed OD intermediate. The latter feature was isolated and analysis of TPD spectra revealed that the D2O production reaction was approximately half-order in total oxygen coverage with a pre-exponential factor ranging from υd=4+/-1*1016 to 5+/-2*1018 molecules1/2 cm-1 s-1 and activation energy Ea=9.7+/-0.1 to 11.5+/-0.1 kcal mol-1 for initial coverage ranging from θ0=0.04 to 0.25 ML. Coadsorption studies of OD and H2 revealed that H atoms drive reactions with adsorbed OD at TS ca. 180 K to form all three water isotopes: D2O, HDO, and H2O. Oxygen (O2) TPD spectra contained three desorption features (TS=700 K, 735 K, and 790 K). The relative abundance of O2 from these three features was virtually the same in all low temperature (TS=143 K) TPD experiments. At elevated dosing temperatures (TS=223 K) the two features at TS=700 K and 790 K could be selectively titrated from the surface by hydrogen. The presence of hydrogen prior to OD exposure at this elevated temperature prevented the accumulation of oxygen on the surface. The implications of these observations on our mechanistic understanding of the low temperature (TS210K) water reaction are discussed.

Dynamics of OH and OD radical reactions with HI and GeH4 as studied by infrared chemiluminescence of the H2O and HDO products

Butkovskaya,Setser

, p. 5028 - 5042 (1996)

The infrared chemiluminescence of vibrationally excited H2O and HDO from the highly exothermic reactions of OH and OD radicals with HI and GeH4 was observed in the 2200-5500 cm-1 range. The experiments utilized a fast-flow reactor with 0.3-1 Torr of Ar carrier gas at 300 K; the OH(OD) radicals were produced via the H(D)+NO2 reaction and the H or D atoms were generated by a discharge in a H2(D2)Mr mixture. The H2O and HOD vibrational distributions were determined by computer simulation of the emission spectra in the 2200-3900 cm-1 range. The total vibrational energy released to H2O and HOD molecules is, respectively, 〈fυ〉 = 0.36 and 0.41 from HI and 〈fυ〉 = 0.46 and 0.51 from GeH4. These values are significantly smaller than for the reactions of OH and OD with HBr, 〈fυ〉 = 0.61 and 0.65. The populations of the O-H stretching vibration of HOD and the collisionally coupled υ1 and υ3 stretching modes of H2O decrease with increasing vibrational energy. In contrast, the vibrational distribution from the HBr reaction is inverted. The bending mode distributions in all stretching states of H2O and HOD extend to the thermodynamic limit of each reaction. A surprisal analysis was made for H2O(HOD) distributions from the title reactions and compared with that for OH(OD)+HBr. The surprisal analysis tends to confirm that the dynamics for the HI and GeH4 reactions differ from the HBr reaction. The HI reaction may proceed mainly via addition-migration, while the GeH4 reaction may involve both direct abstraction and addition-migration. A rate constant for the OH+GeH4→H2O+GeH3 reaction was evaluated by comparing the H2O emission intensities with that of the OH+HBr→H2O+Br reaction, kGeH4/kHBr = 6.5 ± 0.9. Secondary kinetic-isotope effects, kOH/kOD = 1.4 ± 0.1, 1.0±0.2, and 1.3±0.2, were determined for reactions of OH and OD with GeH4, HI, and HBr, respectively, by comparing the relative H2O and HOD emission intensities.

Kinetic Study of the Reaction of OH with H2 and D2 from 250 to 1050 K

Ravishankara, A.R.,Nicovich, J. M.,Thompson, R. L.,Tully, F. P.

, p. 2498 - 2503 (1981)

Absolute rate coefficients for the reactions OH + H2 -> H2O + H (k1) and OH + D2 -> DHO + D (k2) have been measured between 250 and 1050 K by using the flash photolysis-resonance fluorescence technique.The adaptation of the flash pho

Purlee, E. L.

, p. 263 - 272 (1959)

Urey, H. C.,Teal, G. K.

, p. 34 - 94 (1935)

Excitation function and reaction threshold studies of isotope exchange reactions: H + D2 → D + HD and H + D2O → D + HOD

Brownsword, Richard A.,Hillenkamp, Matthias,Laurent, Thomas,Volpp, Hans-Robert,Wolfrum, Jürgen,Vatsa, Rajesh K.,Yoo, Hee-Soo

, p. 6448 - 6454 (1997)

Laser photolysis of H2S at 248 nm and at 193 nm was used to generate nonequilibrium distributions of translationally energetic hydrogen atoms at high dilution in a flowing moderator gas (N2 or Ar). The pulsed laser photolysis/laser-induced fluorescence pump-and-probe method allowed the measurement of the line shapes of the moderated H atom Doppler profiles as well as the concentrations of D atoms produced in the reactive collisions between the H atoms and D2 or D2O reagents. H and D atoms were detected with sub-Doppler resolution via (2p2P ← 1s2S) laser-induced fluorescence. The measured H atom Doppler profiles were used to describe the evolution of the initially generated nascent nonequilibrium H atom speed distribution toward its equilibrium Maxwell-Blotzmann form. In this way the excitation function and reaction threshold for the reactions H + D2 → HD + D and H + D2O → HOD + D could be determined for the first time from the measured nonequilibrium D atom formation rates and single-collision absolute reaction cross sections measured at higher collision energies.

Lin, C. T.

, p. 347 - 353 (1986)

Fast reactions of atom substitution from polyatomic molecules and solid salts by thermally equilibrated atomic reactants

Azatyan

, p. 149 - 163 (2002)

A new class of fast thermal gas-phase reactions of the direct substitution of atoms in polyatomic molecules by atomic reactants is discovered. The Arrhenius parameters are determined for the reactions of atomic deuterium with a number of hydrogen-containing compounds, occurring via the direct substitution of hydrogen atoms and via the abstraction of hydrogen atoms. Fast substitution of alkali metal atoms from the crystals of their salts for the reaction chain carriers of hydrogen flames is found. The importance of reactions of these types in chain combustion is demonstrated. The kinetic isotope effects of hydrogen atom abstraction from hydrocarbon molecules by hydrogen and deuterium atoms are studied. A method for the kinetic studies of free atoms and radicals is developed, which takes into account the role of longitudinal diffusion in the jet and does not require the knowledge of the concentrations of atoms and radicals or the rate constants of other reactions.

Horiuti, J.,Polanyi, M.

, p. 819 - 819 (1933)

A Kinetic Study of OH Radical Reactions with Methane and Perdeuterated Methane

Dunlop, James R.,Tully, Frank P.

, p. 11148 - 11150 (1993)

We measured absolute rate coefficients for the reactions of the hydroxyl raical with methane (k1) and methane-d4 (k2) using the laser photolysis/laser-induced fluorescence technique.We characterized k1 and k2 over the temperature range 293-800 K at pressures between 400 and 750 Torr of helium.We find excellent agreement between our results and the recent determinations of k1 at lower temperatures by Vaghjiani and Ravishankara.The measured rate coefficients, in the units cm3 molecule-1 s-1, fit well to the three-parameter expressions k1(T)=9.65*10-20T2.58 exp(-1082/T) and k2(T)=8.70*10-22T3.23 exp(-1334/T).The kinetic isotope effect for abstraction of the H and D atoms varies from 6.75 at 293 K to 1.96 at 800 K.We compare our results to recently reported calculations by Melissas and Truhlar.

Investigation of NO reduction by H2 on Pd monolith with transient and isotopic exchange techniques: II. H2/D2 exchange in the reduction of NO

Rahkamaa-Tolonen,Salmi,Murzin,Barreto Dillon,Lassi,Keiski

, p. 30 - 38 (2002)

The kinetics and mechanism of catalytic reduction of nitrogen oxide (NO) by hydrogen on an alumina-based palladium monolith were studied under atmospheric pressure at 155°C. Transient kinetic experiments, as well as isotopic exchange techniques, were appl

Bunn, D.,Dainton, F. S.,Salmon, G. A.,Hardwick, T. J.

, p. 1760 - 1767 (1959)

Diffusion of HDO in pure and acid-doped ice films

Oxley, Susan P.,Zahn, Caitlin M.,Pursell, Christopher J.

, p. 11064 - 11073 (2006)

In these experiments, a few bilayers of D2O were vapor-deposited on a pure crystalline H2O ice film or an ice film doped with a small amount of HCl. Upon deposition, H/D isotopic exchange quickly converted the D2O layer into an HDO-rich mixture layer. Infrared absorption spectroscopy followed the changes of the HDO from the initial HDO mixture layer to HDO isolated in the H2O ice film. This was possible because isolated HDO in H2O ice has a unique, sharp peak in the O-D stretch region that can be distinguished from the broad peak due to the initial HDO mixture layer. The absorbance of isolated HDO displayed first-order kinetics and was attributed to diffusion of HDO from the HDO-rich mixture layer into the underlying H2O ice film. While negligible diffusion was observed for pure ice films and for ice films with HCl concentrations up to 1 × 10 -4 mole fraction, diffusion of HDO occurred for higher concentrations of (2-20) × 10-4 mole fraction HCl with a concentration- independent rate constant. The diffusion under these conditions followed Arrhenius behavior for T = 135-145 K yielding Ea = 25 ± 5 kJ/mol. The mechanism for the HDO diffusion involves either (i) molecular self-diffusion or (ii) long-range H/D diffusion by a series of multiple proton hop and orientational turn steps. While these spectroscopic results compare favorably with recent studies of molecular self-diffusion in low-temperature ice films, the diffusion results from all the ice film studies at low temperatures (ca. T 220 K). A comparison and discussion of the various diffusion studies are included in this report.

Coordination-Induced N-H Bond Weakening in a Molybdenum Pyrrolidine Complex: Isotopic Labeling Provides Insight into the Pathway for H2Evolution

Bezdek, Máté J.,Pelczer, István,Chirik, Paul J.

supporting information, p. 3050 - 3059 (2020/09/02)

The synthesis and characterization of a cationic molybdenum pyrrolidine complex are described that exhibits significant coordination-induced N-H bond weakening. The N-H bond dissociation free energy (BDFE) of the coordinated pyrrolidine in [(PhTpy)(PPh2Me)2Mo(NH(pyrr))][BArF24] ([1-NH(pyrr)]+PhTpy = 4′-Ph-2,2′,6′,2″-terpyridine, NH(pyrr) = pyrrolidine, ArF24 = [C6H3-3,5-(CF3)2]4) was determined to be between 41 and 51 kcal mol-1 by thermochemical analysis and supported by a density functional theory (DFT) computed value of 48 kcal mol-1. The complex [1-NH(pyrr)]+ underwent proton-coupled electron transfer (PCET) to 2,4,6-tri-tert-butylphenoxyl radical, as well as spontaneous H2 evolution upon gentle heating to furnish the corresponding molybdenum pyrrolidide complex [(PhTpy)(PPh2Me)2Mo(N(pyrr))][BArF24] ([1-N(pyrr)]+). Thermolysis of the deuterated isotopologue [1-ND(pyrr)]+ still produced H2 with concomitant incorporation of the isotopic label into the pyrrolidide ligand in the product [(1-N(pyrr-dn)]+ (n = 0-2), consistent with an H2 evolution pathway involving intramolecular H-H bond formation followed by an intermolecular product-forming PCET step. These observations provide the context for understanding H2 evolution in the nonclassical ammine complex [(PhTpy)(PPh2Me)2Mo(NH3)][BArF24] ([1-NH3]+) and are supported by DFT-computed reaction thermochemistry. Overall, these studies offer rare insight into the H2 formation pathway in nonclassical amine complexes with N-H BDFEs below the thermodynamic threshold for H2 evolution and inform the development of well-defined, thermodynamically potent PCET reagents.