OD Reaction Research Articles

Differential Cross-Sections for the Vibrationally Excited H + HOD(vOH = 1-4) → H2 + OD Reactions.

Using the time-dependent wave-packet approach, we calculate the first fully converged state-to-state differential cross-sections for the H + HOD(vOH = 1-4) → H2 + OD reactions on a highly accurate neural network PES. It is found that, unlike the loss of memory effect observed in the product distributions for low vibrational excitation reactions, high initial OH vibrational excitation significantly influences not only the product vibrational distribution but also the angular distribution. Furthermore, for the H + HOD(vOH = 3,4) reactions, the total integral cross-sections maintain the pronounced oscillatory structures in the J = 0 probabilities at low collision energies, which originate from the prereactive van der Waals resonances. Notably, the product angular distributions exhibit forward-backward peaked behavior at these energies, akin to those observed in the complex-forming system with deep potential wells. This is attributed to the much longer lifetimes of these resonances compared to those of conventional transition state resonances.

High vibrational excitation of the reagent transforms the late-barrier H + HOD reaction into an early-barrier reaction.

Polanyi's rules predict that a late-barrier reaction yields vibrationally cold products; however, experimental studies showed that the H2 product from the late-barrier H + H2O(|04⟩-) and H + HOD(vOH = 4) reactions is vibrationally hot. Here, we report a potential-averaged five-dimensional state-to-state quantum dynamics study for the H + HOD(vOH = 0-4) → H2 + OD reactions on a highly accurate potential energy surface with the total angular momentum J = 0. It is found that with the HOD vibration excitation increasing from vOH = 1 to 4, the product H2 becomes increasingly vibrationally excited and manifests a typical characteristic of an early barrier reaction for vOH = 3 to 4. Analysis of the scattering wave functions revealed that vibrational excitation in the breaking OH bond moves the location of dynamical saddle point from product side to reactant side, transforming the reaction into an early barrier reaction. Interestingly, pronounced oscillatory structures in the total and product vibrational-state-resolved reaction probabilities were observed for the H + HOD(vOH = 3, 4) reactions, in particular at low collision energies, which originate from the Feshbach resonance states trapped in the bending/torsion excited vibrational adiabatic potential wells in the entrance region due to van der Waals interactions.

Isotope Exchange Reaction of OH− Anion with HD at Temperatures from 15 K up to 300 K: Ion Trap Study

This paper presents the results of an experimental study of the reaction of OH− anions with HD molecules leading to the formation of OD− anions. The study’s main goal was to obtain the temperature dependence of the reaction rate coefficient and determine the reaction’s enthalpy. This study was carried out at astrophysically relevant temperatures from 15 to 300 K. The reaction was studied using a temperature-variable cryogenic linear 22-pole radio-frequency ion trap. The rotational temperature of the OH− anions in the ion trap was characterized by near-threshold photodetachment spectroscopy. At 15 K, the measured reaction rate coefficient is 5 × 10−10 cm3 s−1. With increasing temperature, the reaction rate coefficient decreases monotonically to 5 × 10−11 cm3 s−1 at 300 K. Comparing with the previously determined rate coefficient of the reverse reaction of OD− anions with H2, we obtained the temperature dependence of the equilibrium constant. The enthalpy and entropy of the title reaction were determined in the studied temperature range as ΔH = (−23.9 ± 0.7 ± 2.6sys) meV and ΔS = (−8.5 ± 1.2 ± 1.4sys) J mol−1 K−1, respectively.

A Theoretical Kinetic and Classical Dynamic Investigation of CN + OH and CN + OD Reactions on an Interpolated Potential Energy Surface

In the current work, kinetic and dynamic parameters in reactive and non-reactive collisions between CN and OH radicals were investigated upon an interpolated potential energy surface using MP2/6-311G++(d,p) ab-initio method. The total and individual reaction probability and cross-section, for all reactions, were obtained and applied to calculate the rate constant and rate expression. In non-reactive trajectories, the effect of the impact parameter and relative translational energy of particles on the deflection angle was also investigated. To investigate the kinetic isotopic effect, the deuterium was used instead of hydrogen atom to illustrate the effect of mass of attacking radical and target molecule on physical observable such as reaction probability and cross-section

Rate constants and vibrational distributions for water‐forming reactions of OH and OD radicals with thioacetic acid, 1,2‐ethanedithiol and tert‐butanethiol

AbstractReactions of OH and OD radicals with CH3C(O)SH, HSCH2CH2SH, and (CH3)3CSH were studied at 298 K in a fast‐flow reactor by infrared emission spectroscopy of the water product molecules. The rate constants (1.3 ± 0.2) × 10−11 cm3 molecule−1 s−1 for the OD + CH3C(O)SH reaction and (3.8 ± 0.7) × 10−11 cm3 molecule−1 s−1 for the OD + HSCH2CH2SH reaction were determined by comparing the HOD emission intensity to that from the OD reaction with H2S, and this is the first measurement of these rate constants. In the same manner, using the OD + (C2H5)2S reference reaction, the rate constant for the OD + (CH3)3CSH reaction was estimated to be (3.6 ± 0.7) × 10−11 cm3 molecule−1 s−1. Vibrational distributions of the H2O and HOD molecules from the title reactions are typical for H‐atom abstraction reactions by OH radicals with release of about 50% of the available energy as vibrational energy to the water molecule in a 2:1 ratio of stretch and bend modes.

Rate Coefficient Measurements and Theoretical Analysis of the OH + ( E)-CF3CH═CHCF3 Reaction.

Rate coefficients, k, for the gas-phase reaction of the OH radical with ( E)-CF3CH═CHCF3 (( E)-1,1,1,4,4,4-hexafluoro-2-butene, HFO-1336mzz(E)) were measured over a range of temperatures (211-374 K) and bath gas pressures (20-300 Torr; He, N2) using a pulsed laser photolysis-laser-induced fluorescence (PLP-LIF) technique. k1( T) was independent of pressure over this range of conditions with k1(296 K) = (1.31 ± 0.15) × 10-13 cm3 molecule-1 s-1 and k1( T) = (6.94 ± 0.80) × 10-13exp[-(496 ± 10)/ T] cm3 molecule-1 s-1, where the uncertainties are 2σ, and the pre-exponential term includes estimated systematic error. Rate coefficients for the OD reaction were also determined over a range of temperatures (262-374 K) at 100 Torr (He). The OD rate coefficients were ∼15% greater than the OH values and showed similar temperature dependent behavior with k2( T) = (7.52 ± 0.44) × 10-13exp[-(476 ± 20)/ T] and k2(296 K) = (1.53 ± 0.15) × 10-13 cm3 molecule-1 s-1. The rate coefficients for reaction 1 were also measured using a relative rate technique between 296 and 375 K with k1(296 K) measured to be (1.22 ± 0.1) × 10-13 cm3 molecule-1 s-1, in agreement with the PLP-LIF results. In addition, the 296 K rate coefficient for the O3 + ( E)-CF3CH═CHCF3 reaction was determined to be <5.2 × 10-22 cm3 molecule-1 s-1. A theoretical computational analysis is presented to interpret the observed positive temperature dependence for the addition reaction and the significant decrease in OH reactivity compared to the ( Z)-CF3CH═CHCF3 stereoisomer reaction. The estimated atmospheric lifetime of ( E)-CF3CH═CHCF3, due to loss by reaction with OH, is estimated to be ∼90 days, while the actual lifetime will depend on the location and season of its emission. Infrared absorption spectra of ( E)-CF3CH═CHCF3 were measured and used to estimate the 100 year time horizon global warming potentials (GWP) of 32 (atmospherically well-mixed) and 14 (lifetime-adjusted).

Quasi-classical dynamics investigations of the F + D 2 O → DF + OD reaction on a full dimensional accurate potential energy surface

Abstract The influence of vibrational excitations in the fully deuterated water (D2O) reactant on the reaction with the fluorine atom (F) is investigated using the full-dimensional quasi-classical trajectory method on an accurate ground electronic state potential energy surface. The results show that the reactant vibrational excitation in each mode of D2O has very complicated effect on the reactivity. At low collision energy, excitations in all three modes are more effective than collision energy in promoting the reaction, and their efficacies follow this order: symmetric stretching mode > anti-symmetric stretching mode > bending mode. At high collision energies, the efficacies of the bending and the anti-symmetric stretching modes are similar to or slightly less than collision energy, while the symmetric stretching mode is significantly less effective than collision energy. These intricate mode specificities in the F + D2O → DF + OD reaction cannot be rationalized by the sudden vector projection model due to much denser density of states and faster intramolecular vibrational relaxation rate in D2O than in H2O.

Branching Ratios and Vibrational Distributions in Water-Forming Reactions of OH and OD Radicals with Methylamines.

Reactions of OH and OD radicals with (CH3)3N, (CH3)2NH, and CH3NH2 were studied by Fourier transform infrared emission spectroscopy (FTIR) of the water product molecules from a fast-flow reactor at 298 K. The rate constants (4.4 ± 0.5) × 10(-11), (5.2 ± 0.8) × 10(-11), and (2.0 ± 0.4) × 10(-11) cm(3) molecule(-1) s(-1) were determined for OD + (CH3)3N, (CH3)2NH, and CH3NH2, respectively, by comparing the HOD emission intensities to the HOD intensity from the OD reaction with H2S. Abstraction from the nitrogen site competes with abstraction from the methyl group, as obtained from an analysis of the HOD and D2O emission intensities from the OD reactions with the deuterated reactants, (CD3)2NH and CD3NH2. After adjustment for the hydrogen-deuterium kinetic isotope effect, the product branching fractions of the hydrogen abstraction from the nitrogen for di- and monomethylamine were found to be 0.34 ± 0.04 and 0.26 ± 0.05, respectively. Vibrational distributions of the H2O, HOD, and D2O molecules are typical for direct hydrogen atom abstraction from polar molecules, even though activation energies are negative because of the formation of pre-transition-state complexes. Comparison is made to the reactions of hydroxyl radicals with ammonia and with other compounds with primary C-H bonds to discuss specific features of disposal of energy to water product.

Detection of Chlamydia infection in Peromyscus species rodents from sylvatic and laboratory sources.

To determine if Chlamydia muridarum, or other chlamydiae, are enzootic in rodents, we probed a serum bank of wild Peromyscus spp. mice for immunoglobulin G-antibody reactivity to ultraviolet light-inactivated C. muridarum elementary bodies (EBs) using an enzyme-linked immunoassay. Applying a cut-off for a positive reaction of OD(405) nm = 0.1 at a 1:20 dilution, we found titratable antibody reactivity in 190 of 247 specimens surveyed (77%, mean OD(405) = 0.33 ± 0.26, range = 0.11-1.81, median = 0.25). In addition, serum samples were obtained from a colony of specific pathogen-free Peromyscus spp. maintained at the University of South Carolina and six of 12 samples were reactive (50%, mean OD(405) = 0.19 +/- 0.08, range = 0.1-0.32, median = 0.18). Lastly, 40 additional wild Peromyscus spp. were captured in a disparate region of Midwestern USA and 22 serum specimens were reactive (55%, mean OD(405) = 0.22 +/- 0.11, range = 0.1-0.48, median = 0.2). Specificity of selected reactive sera for chlamydial antigen was confirmed on Western blot using resolved purified EBs as the detecting antigen. From tissues removed from several mice at necropsy, the gene for chlamydial 16S ribosomal ribonucleic acid (rRNA) was amplified by polymerase chain reaction (PCR). Positive samples of 16S rRNA were subjected to additional PCR for the major outer membrane protein gene (ompA). The amplicons of three select ompA positive samples were sequenced with ≥99% homology with C. muridarum. Our findings indicate that chlamydial infection is enzootic for Peromyscus spp., and that C. muridarum, or a closely related species or strain, is likely the agent in the tested rodent species.

Branching ratios in reactions of OH radicals with methylamine, dimethylamine, and ethylamine.

The branching ratios for the reaction of the OH radical with the primary and secondary alkylamines: methylamine (MA), dimethylamine (DMA), and ethylamine (EA), have been determined using the technique of pulsed laser photolysis-laser-induced fluorescence. Titration of the carbon-centered radical, formed following the initial OH abstraction, with oxygen to give HO2 and an imine, followed by conversion of HO2 to OH by reaction with NO, resulted in biexponential OH decay traces on a millisecond time scale. Analysis of the biexponential curves gave the HO2 yield, which equaled the branching ratio for abstraction at αC-H position, r(αC-H). The technique was validated by reproducing known branching ratios for OH abstraction for methanol and ethanol. For the amines studied in this work (all at 298 K): r(αC-H,MA) = 0.76 ± 0.08, r(αC-H,DMA) = 0.59 ± 0.07, and r(αC-H,EA) = 0.49 ± 0.06 where the errors are a combination in quadrature of statistical errors at the 2σ level and an estimated 10% systematic error. The branching ratios r(αC-H) for OH reacting with (CH3)2NH and CH3CH2NH2 are in agreement with those obtained for the OD reaction with (CH3)2ND (d-DMA) and CH3CH2ND2 (d-EA): r(αC-H,d-DMA) = 0.71 ± 0.12 and r(αC-H,d-EA) = 0.54 ± 0.07. A master equation analysis (using the MESMER package) based on potential energy surfaces from G4 theory was used to demonstrate that the experimental determinations are unaffected by formation of stabilized peroxy radicals and to estimate atmospheric pressure yields. The branching ratio for imine formation through the reaction of O2 with α carbon-centered radicals at 1 atm of N2 are estimated as r(CH2NH2) = 0.79 ± 0.15, r(CH2NHCH3) = 0.72 ± 0.19, and r(CH3CHNH2) = 0.50 ± 0.18. The implications of this work on the potential formation of nitrosamines and nitramines are briefly discussed.

Gas-Phase Reactions of OH with Methyl Amines in the Presence or Absence of Molecular Oxygen. An Experimental and Theoretical Study

The rate coefficients for the reaction of OH with the alkyl amines: methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), and ethylamine (EA) have been determined using the technique of pulsed laser photolysis with detection of OH by laser-induced fluorescence as a function of temperature from 298 K to ∼600 K. The rate coefficients (10(11) × k/cm(3) molecule(-1) s(-1)) at 298 K in nitrogen bath gas (typically 5-25 Torr) are: k(OH+MA) = 1.97 ± 0.11, k(OH+DMA) = 6.27 ± 0.63, k(OH+TMA) = 5.78 ± 0.48, k(OH+EA) = 2.50 ± 0.13. The reactions all show a negative temperature dependence which can be characterized as: k(OH+MA) = (1.889 ± 0.053) × 10(-11)(T/298 K)(-(0.56±0.10)), k(OH+DMA) = (6.39 ± 0.35) × 10(-11)(T/298 K)(-(0.75±0.18)), k(OH+TMA) = (5.73 ± 0.15) × 10(-11)(T/298 K)(-(0.71±0.10)), and k(OH+EA) = (2.54 ± 0.08) × 10(-11)(T/298 K)(-(0.68±0.10)). OH and OD reactions have very similar kinetics. Potential energy surfaces (PES) for the reactions have been characterized at the MP2/aug-cc-pVTZ level and improved single point energies of stationary points obtained in CCSD(T) and CCSD(T*)-F12a calculations. The PES for all reactions are characterized by the formation of pre- and post-reaction complexes and submerged barriers. The calculated rate coefficients are in good agreement with experiment; the overall rate coefficients are relatively insensitive to variations of the barrier heights within typical chemical accuracy, but the branching ratios vary significantly. The rate coefficients for the reactions of OH/OD with MA, DMA, and EA do not vary with added oxygen, but for TMA a significant reduction in the rate coefficient is observed consistent with OH recycling from a chemically activated peroxy radical. OH regeneration is pressure-dependent and is not significant at 298 K and atmospheric pressure, but the efficiency of recycling increases strongly with temperature. The PES for OH recycling have been calculated. There is evidence that the primary process in TMA photolysis at 248 nm is the loss of H atoms.

Influence of ro-vibrational and isotope effects on the dynamics of the C(3 P)+ OD(X 2Π) → CO(X 1 Σ+) + D(2 S) reaction

The C(3 P)+OD(X 2Π) reaction has been studied by means of quantum mechanical real wave packet (RWP) and quasiclassical trajectory (QCT) methodologies on the ground potential energy surface of Zanchet et al. [J. Phys. Chem. A 110, 12017 (2006)]. Initial state selected total reaction probabilities at J = 0 total angular momentum have been calculated for a wide range of collision energies. Product state-resolved integral cross-sections at selected collision energies and excitation functions have been determined from the RWP calculations using the J-shifting approximation and from QCT calculations. State-specific and thermal rate coefficients have been calculated using both methodologies up to 500 K. The effect of reagent rotational excitation on the dynamics for the C(3 P)+OH(X 2Π) and C(3 P)+OD(X 2Π) reactions has been investigated and interesting discrepancies between the QCT and RWP results have been found. The RWP results are found to be in an overall good agreement with the corresponding QCT results, although the QCT integral cross-section and rate coefficients are slightly smaller than those obtained from the RWP calculations.

Collision energy dependence for the Br formation in the reaction of OD+HBr

The collision energy dependence for Br(2P3/2) atom formation in the reaction of OD + HBr has been investigated from 0.05 to 0.26 eV using a crossed molecular beam experiment. OD radicals were selected as the single rotational state in the upper state of Λ-doubling of using a 1 m electric hexapole field. Br atoms were detected by the vacuum ultraviolet (VUV) laser-induced fluorescence technique. We find that the reaction cross-section decreases, increasing the collision energy. This negative collision energy dependence suggests that there is no barrier on the potential energy surface for the formation pathway considered. Results were compared with those previously reported for the OH + HBr reaction system. We find that the ratio of the reaction cross-section of σ(OD)/σ(OH) shows values larger than one and an increasing tendency when collision energy increases. The collision energy dependence observed is explained in terms of the zero-point energy differences and the rotational periods of OD and OH, which may be related to the time for the proper reorientation of the OH radical prior to the reaction.

Nonadiabatic reactive scattering in atom+triatom systems: Nascent rovibronic distributions in F+H2O→HF+OH

Crossed supersonic jet studies of F + H(2)O --> HF + OH((2)Pi(3/2),(2)Pi(1/2)) have been performed under low density, single collision conditions at E(com) = 6(2) kcal/mol, yielding rotational, vibrational, and spin-orbit state distributions in the nascent OH product by laser induced fluorescence methods. The lowest reaction barriers on the ground and first excited electronic surfaces are DeltaE approximately 4 kcal/mol and DeltaE approximately 25 kcal/mol, correlating with OH((2)Pi(3/2)) and OH((2)Pi(1/2)), respectively. Although only reactions on the ground state potential are Born-Oppenheimer allowed at the experimental collision energies, both ground and excited spin-orbit OH products are observed in a (2)Pi(3/2):(2)Pi(1/2) = 69(1)%:31(1)% branching ratio. This indicates the presence of strong nonadiabatic surface hopping interactions, in agreement with previous results for the F + D(2)O --> DF + OD reaction. Despite clear differences in the rotational distributions between F + H(2)O and F + D(2)O isotopic reactions, the overall electronic branching into spin-orbit manifolds is nearly identical for both OH and OD products. Furthermore, when plotted versus total electronic + rotational energy, the nascent OH and OD populations each lie on single curves, with pronounced kinks in the Boltzmann plots suggestive of microscopic branching in the reaction dynamics. Such an equivalence of electronic and rotational energy release in the OH/OD products is consistent with predominantly nonadiabatic processes taking place in the immediate post-transition state region rather than asymptotically in the exit channel.

Singlet and triplet state dynamics of charge and hydride transfer reactions of OD + ( X3Σ −) with propyne

We report a crossed beam study of the title reactions in the collision energy range from 0.45 to 1.23 eV (43–119 kJ/mol). Both reactions are exoergic and proceed as direct processes on a time scale much less than the rotational period of the transient association complex of approaching reactants. The charge transfer process takes place with zero momentum transfer. Density Functional Theory calculations of the structures of reactive intermediates show that a plausible pathway for hydride transfer involves initial charge transfer on a triplet surface, followed by intersystem crossing to the singlet manifold. This process is followed by rapid hydrogen atom transfer to form an intermediate that dissociates smoothly to products. The kinematics of the heavy + light-heavy mass combination result in mixed energy release at the lowest collision energy, in which both the breaking and forming bonds are extended, while at higher collision energies, the incremental translational energy in the reactants appears preferentially in product translation, consistent with induced repulsive energy release.

Hydride transfer reaction dynamics of OD++C3H6

The hydride transfer reaction between OD+ and C3H6 has been studied experimentally and theoretically over the center of mass collision energy range from 0.21 to 0.92 eV using the crossed beam technique and density functional theory calculations. The center of mass flux distributions of the product ions at three different energies are highly asymmetric, with maxima close to the velocity and direction of the precursor propylene beam, characteristic of direct reactions. In the hydride transfer process, the entire reaction exothermicity is transformed into product internal excitation, consistent with mixed energy release in which the hydride ion is transferred with both the breaking and forming bonds extended. At higher collision energies, at least 85% of the incremental translational energy appears in product translation, providing a clear example of induced repulsive energy release. Compared to the related reaction of OD+ with C2H4, reaction along the pathway initiated by addition of OD+ to the C=C bond in propylene has a critical bottleneck caused by the torsional motion of the methyl substituent on the double bond. This bottleneck suppresses reaction through an intermediate complex in favor of direct hydride abstraction. Hydride abstraction appears to be a sequential process initiated by electron transfer in the triplet manifold, followed by rapid intersystem crossing and subsequent hydrogen atom transfer to form ground state allyl cation and HOD.

Experimental and Theoretical Studies of the Kinetics of the Reactions of OH and OD with 2-Methyl-3-buten-2-ol between 300 and 415 K at Low Pressure

The rate constants for the reactions of OH and OD with 2-methyl-3-buten-2-ol (MBO) have been measured at 2, 3, and 5 Torr total pressure over the temperature range 300-415 K using a discharge-flow system coupled with laser induced fluorescence detection of OH. The measured rate constants at room temperature and 5 Torr for the OH + MBO reaction in the presence of O2 and the OD + MBO reaction are (6.32 +/- 0.27) and (6.61 +/- 0.66) x 10(-11) cm3 molecule(-1) s(-1), respectively, in agreement with previous measurements at higher pressures. However, the rate constants begin to show a pressure dependence at temperatures above 335 K. An Arrhenius expression of k0 = (2.5 +/- 7.4) x 10(-32) exp[(4150 +/- 1150)/T] cm6 molecule(-2) s(-1) was obtained for the low-pressure-limiting rate constant for the OH + MBO reaction in the presence of oxygen. Theoretical calculations of the energetics of the OH + MBO reaction suggest that the stability of the different HO-MBO adducts are similar, with predicted stabilization energies between 27.0 and 33.4 kcal mol(-1) relative to the reactants, with OH addition to the internal carbon predicted to be 1-4 kcal mol(-1) more stable than addition to the terminal carbon. These stabilization energies result in estimated termolecular rate constants for the OH + MBO reaction using simplified calculations based on RRKM theory that are in reasonable agreement with the experimental values.

Experimental and theoretical studies of the kinetics of the reactions of OH and OD with acetone and acetone- d6 at low pressure

The kinetics of the reactions of OH and OD with acetone and acetone- d 6 were studied from 2–5 Torr and 258–402 K using a discharge flow system with laser induced fluorescence or resonance fluorescence detection of the OH radical. The rate constants at 300 K for the reaction of OH with acetone and acetone- d 6 were (1.73 ± 0.06) × 10 −13 and (3.36 ± 0.32) × 10 −14 cm 3 molecule −1 s −1, respectively. The rate constants at 300 K for the reaction of OD with acetone and acetone- d 6 were (2.87 ± 0.22) × 10 −13 and (3.69 ± 0.12) × 10 −14 cm 3 molecule −1 s −1, respectively. Above room temperature, the temperature dependence of the rate constants for the OH + acetone and acetone- d 6 display Arrhenius behavior and are described by the equations k H( T) = (3.92 ± 0.81) × 10 −12 exp(−938 ± 70/ T) and k D( T) = (8.19 ± 1.45) × 10 −12 exp(−1647 ± 58/ T) cm 3 molecule −1 s −1 for acetone and acetone- d 6, respectively. Measurements of k H and k D below room temperature begin to display non-Arrhenius behavior, consistent with previous measurements at higher pressures. Theoretical calculations of the kinetic isotope effect as a function of temperature are in good agreement with the experimental measurements using a hydrogen abstraction mechanism that proceeds through a hydrogen-bonded complex.

Experimental and theoretical studies of charge transfer and hydride transfer in the reactions of OD + and C 2H 4

We present a crossed beam and density functional theory (DFT) study of the dynamics of charge transfer and hydride transfer in collisions of OD + with C 2H 4 at relative collision energies between 19.3 and 102 kJ mol −1 (0.20–1.06 eV). Charge transfer to form C 2H 4 + is a direct process occurring through large impact parameters. A comparison of the internal energy distributions of reaction products with the photoelectron spectrum of C 2H 4 is consistent with a Franck–Condon picture for long distance electron transfer. Charge transfer with H/D rearrangement to form C 2H 3D + + OH does not occur, unlike the related system D 2O + + C 2H 4, in which comparable amounts of C 2H 4 + and C 2H 3D + are observed. This difference is accounted for by the significantly smaller proton affinity of OH relative to H 2O. Reactive processes are initiated by the formation of a protonated oxirane triplet diradical, which undergoes intersystem crossing to the singlet manifold. Formation of C 2H 3 + + HOD, nominally a hydride transfer reaction, is shown to occur at the lowest collision energy through transient singlet intermediates in which the timescale for rate-limiting hydrogen atom migration corresponds to a significant fraction of a rotational period. Formation of hydride transfer products is sufficiently exothermic (ΔH = −489 kJ mol −1) that a fraction of the C 2H 3 + products may be formed above the dissociation threshold to C 2H 2 +. Increasing collision energy results in enhanced yields of C 2H 2 + relative to C 2H 3 +, consistent with unimolecular decay of the most highly excited C 2H 3 + products. However, the very small translational energy releases at all collision energies also require significant vibrational excitation in the HOD products; the most probable internal excitation in HOD is approximately 60 kJ mol −1 at all collision energies.

Infrared Chemiluminescence from Water‐Forming Reactions: Characterization of Dynamics and Mechanisms

AbstractFor Abstract see ChemInform Abstract in Full Text.