Adiabatic and nonadiabatic dynamics in the CH{sub 3}(CD{sub 3})+HCl reaction

Journal Article · Wed May 14 04:00:00 EDT 2008 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.2913516· OSTI ID:21104045

Retail, Bertrand; Pearce, Julie K; Greaves, Stuart J; Rose, Rebecca A; Orr-Ewing, Andrew J ^[1]

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1. School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS (United Kingdom)

The scattering dynamics leading to the formation of Cl ({sup 2}P{sub 3/2}) and Cl* ({sup 2}P{sub 1/2}) products of the CH{sub 3}+HCl reaction (at a mean collision energy <E{sub coll}>=22.3 kcal mol{sup -1}) and the Cl ({sup 2}P{sub 3/2}) products of the CD{sub 3}+HCl reaction (at <E{sub coll}>=19.4 kcal mol{sup -1}) have been investigated by using photodissociation of CH{sub 3}I and CD{sub 3}I as sources of translationally hot methyl radicals and velocity map imaging of the Cl atom products. Image analysis with a Legendre moment fitting procedure demonstrates that, in all three reactions, the Cl/Cl* products are mostly forward scattered with respect to the HCl in the center-of-mass (c.m.) frame but with a backward scattered component. The distributions of the fraction of the available energy released as translation peak at f{sub t}=0.31-0.33 for all the reactions, with average values that lie in the range <f{sub t}>=0.42-0.47. The detailed analysis indicates the importance of collision energy in facilitating the nonadiabatic transitions that lead to Cl* production. The similarities between the c.m.-frame scattering and kinetic energy release distributions for Cl and Cl* channels suggest that the nonadiabatic transitions to a low-lying excited potential energy surface (PES) correlating to Cl* products occur after passage through the transition state region on the ground-state PES. Branching fractions for Cl* are determined to be 0.14{+-}0.02 for the CH{sub 3}+HCl reaction and 0.20{+-}0.03 for the CD{sub 3}+HCl reaction. The difference cannot be accounted for by changes in collision energy, mass effects, or vibrational excitation of the photolytically generated methyl radical reagents and instead suggests that the low-frequency bending modes of the CD{sub 3}H or CH{sub 4} coproduct are important mediators of the nonadiabatic couplings occurring in this reaction system.

• OSTI ID: 21104045
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 18 Vol. 128; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
BRANCHING RATIO
CENTER-OF-MASS SYSTEM
CHLORINE IONS
COLLISIONS
DEUTERIUM COMPOUNDS
DISSOCIATION
EXCITED STATES
GROUND STATES
HYDROCHLORIC ACID
IMAGE PROCESSING
KINETIC ENERGY
METHANE
METHYL IODIDE
METHYL RADICALS
PHOTOLYSIS
POTENTIAL ENERGY