Kinetics and mechanisms of the reaction of CH with H2O

Bergeat, Astrid; Moisan, Sandy; Méreau, Raphaël; Loison, Jean‐Christophe

doi:10.1016/j.cplett.2009.07.080

Cited by 30 publications

(36 citation statements)

References 22 publications

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“…Hydroxymethyl radicals or their structural isomers, the methoxy radicals, are implicated as intermediates in the O + CH 3 and CH + H 2 O reactions. [3][4][5][6] Previous experimental and theoretical work on the photophysics and photochemistry of the hydroxymethyl radical focused on its excited Rydberg electronic states and the involvement of conical intersections. [7][8][9][10] Vibrational excitation and predissociation of CH 2 OH in the ground electronic state has received much less attention because of experimental difficulties.…”

Section: Introductionmentioning

confidence: 99%

Overtone-induced dissociation and isomerization dynamics of the hydroxymethyl radical (CH2OH and CD2OH). I. A theoretical study

Kamarchik

Rodrigo

Bowman

et al. 2012

The Journal of Chemical Physics

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The dissociation of the hydroxymethyl radical, CH(2)OH, and its isotopolog, CD(2)OH, following the excitation of high OH stretch overtones is studied by quasi-classical molecular dynamics calculations using a global potential energy surface (PES) fitted to ab initio calculations. The PES includes CH(2)OH and CH(3)O minima, dissociation products, and all relevant barriers. Its analysis shows that the transition states for OH bond fission and isomerization are both very close in energy to the excited vibrational levels reached in recent experiments and involve significant geometry changes relative to the CH(2)OH equilibrium structure. The energies of key stationary points are refined using high-level electronic structure calculations. Vibrational energies and wavefunctions are computed by coupled anharmonic vibrational calculations. They show that high OH-stretch overtones are mixed with other modes. Consequently, trajectory calculations carried out at energies about ~3000 cm(-1) above the barriers reveal that despite initial excitation of the OH stretch, the direct OH bond fission is relatively slow (10 ps) and a considerable fraction of the radicals undergoes isomerization to the methoxy radical. The computed dissociation energies are: D(0)(CH(2)OH → CH(2)O + H) = 10,188 cm(-1), D(0)(CD(2)OH → CD(2)O + H) = 10,167 cm(-1), D(0)(CD(2)OH → CHDO + D) = 10,787 cm(-1). All are in excellent agreement with the experimental results. For CH(2)OH, the barriers for the direct OH bond fission and isomerization are: 14,205 and 13,839 cm(-1), respectively.

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Section: Introductionmentioning

confidence: 99%

Overtone-induced dissociation and isomerization dynamics of the hydroxymethyl radical (CH2OH and CD2OH). I. A theoretical study

Kamarchik

Rodrigo

Bowman

et al. 2012

The Journal of Chemical Physics

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“…The CH 2 OH and its less stable isomer, CH 3 O, are relevant to atmospheric and combustion chemistry, being implicated as intermediates in reactions such as O + CH 3 and CH + H 2 O. [1][2][3][4] CH 2 OH and CD 2 OH also play an important role in the unusual deuterium enrichment of interstellar methanol. 5 The high-level electronic structure calculations reported in Part I (Ref.…”

Section: Introductionmentioning

confidence: 99%

Overtone-induced dissociation and isomerization dynamics of the hydroxymethyl radical (CH2OH and CD2OH). II. Velocity map imaging studies

Ryazanov

Rodrigo

Reisler

2012

The Journal of Chemical Physics

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The dissociation of the hydroxymethyl radical, CH(2)OH, and its isotopolog, CD(2)OH, following excitation in the 4ν(1) region (OH stretch overtone, near 13,600 cm(-1)) was studied using sliced velocity map imaging. A new vibrational band near 13,660 cm(-1) arising from interaction with the antisymmetric CH stretch was discovered for CH(2)OH. In CD(2)OH dissociation, D atom products (correlated with CHDO) were detected, providing the first experimental evidence of isomerization in the CH(2)OH ↔ CH(3)O (CD(2)OH ↔ CHD(2)O) system. Analysis of the H (D) fragment kinetic energy distributions shows that the rovibrational state distributions in the formaldehyde cofragments are different for the OH bond fission and isomerization pathways. Isomerization is responsible for 10%-30% of dissociation events in all studied cases, and its contribution depends on the excited vibrational level of the radical. Accurate dissociation energies were determined: D(0)(CH(2)OH → CH(2)O + H) = 10,160 ± 70 cm(-1), D(0)(CD(2)OH → CD(2)O + H) = 10,135 ± 70 cm(-1), D(0)(CD(2)OH → CHDO + D) = 10,760 ± 60 cm(-1).

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“…The electronic degeneracy factors are calculated by applying the spin and orbital correlation rules to the potential energy surfaces (PESs) that correlate the separated reactants with the separated products. To evaluate the branching ratio, we performed statistical calculations of the microcanonical rate constants of the various steps of the mechanisms (Bergeat et al 2009). Quantum chemical calculations using the gaussian 09 software package were performed at the M06‐2X/cc‐pVTZ level to provide all relevant geometries, frequencies and rotational constants used for kinetic calculations.…”

Section: Introductionmentioning

confidence: 99%

“…The electronic degeneracy factors are calculated by applying the spin and orbital correlation rules to the potential energy surfaces that correlate the separated reactants with the separated products. To evaluate branching ratio, we performed statistical calculations of the microcanonical rate constants of the various steps of the mechanisms (Bergeat et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Review of OCS gas-phase reactions in dark cloud chemical models

Loison

Halvick

Bergeat

et al. 2012

Monthly Notices of the Royal Astronomical Society

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The association reaction S + CO {\to} OCS + hnu has been identified as being particularly important for the prediction of gas-phase OCS abundances by chemical models of dark clouds. We performed detailed ab-initio calculations for this process in addition to undertaking an extensive review of the neutral-neutral reactions involving this species which might be important in such environments. The rate constant for this association reaction was estimated to be several orders of magnitude smaller than the one present in current astrochemical databases. The new rate for this reaction and the introduction of other processes, notably OH + CS {\to} OCS + H and C + OCS {\to} CO + CS, dramatically changes the OCS gas-phase abundance predicted by chemical models for dark clouds. The disagreement with observations in TMC-1 (CP) and L134N (N), suggests that OCS may be formed on grain surfaces as is the case for methanol. The observation of solid OCS on interstellar ices supports this hypothesis.Comment: Accepted for publication in MNRA

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Kinetics and mechanisms of the reaction of CH with H2O

Cited by 30 publications

References 22 publications

Overtone-induced dissociation and isomerization dynamics of the hydroxymethyl radical (CH2OH and CD2OH). I. A theoretical study

Overtone-induced dissociation and isomerization dynamics of the hydroxymethyl radical (CH2OH and CD2OH). I. A theoretical study

Overtone-induced dissociation and isomerization dynamics of the hydroxymethyl radical (CH2OH and CD2OH). II. Velocity map imaging studies

Review of OCS gas-phase reactions in dark cloud chemical models

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