Unimolecular dynamics of Cl-⋯CH3Cl intermolecular complexes formed by Cl-+CH3Cl association

Gilles H. Peslherbe, Haobin Wang, William L. Hase

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A previous trajectory study of the dissociation of Cl -⋯CH3Cl complexes formed by Cl-+CH 3Cl association is further analyzed to determine (1) the relationship between classical and quantum Rice-Ramsperger-Kassel-Marcus (RRKM) rate constants for Cl-⋯CH3Cl→Cl-+CH 3Cl dissociation; (2) the importance of anharmonicity in calculating the RRKM dissociation rate constant; (3) the role of angular momentum in interpreting the trajectory distribution N(t)/N(0) of Cl -⋯CH3Cl complexes versus time; and (4) the pressure-dependent collision-averaged rate constant k(ω,E) for Cl -⋯CH3Cl dissociation. It is found that only the low-frequency intermolecular modes of Cl-⋯CH3Cl are initially excited by Cl-+CH3Cl association. Classical and quantum RRKM rate constants for dissociation of this intermolecular complex are in excellent agreement. Anharmonicity lowers the rate constant by a factor of 4-8 from its harmonic value. The dissociation rate for the long-time tail of the trajectory N(t)/N(0) distribution is much smaller than predicted by a RRKM model, which accurately treats angular momentum. It is suggested that the long-lived trajectories may arise from motion on vague tori. The trajectory collision-averaged rate constant k(ω,E) is in agreement with an experimental study at 300 K.

Original languageEnglish
Pages (from-to)5626-5635
Number of pages10
JournalThe Journal of Chemical Physics
Issue number14
StatePublished - 1995


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