An ab initio quasi-classical direct dynamics investigation of the F + C2H4 → C2H3F + H product energy distributions

Kim Bolton, H. Bernhard Schlegel, William L. Hase, Kihyung Song

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A direct dynamics technique, using energies, forces and second derivatives calculated at the UHF/6-31G* level of theory, was used to investigate product energy distributions of the F + C2H4 → C2H3F + H collision reaction. The shifting and broadening of the product translational energy distribution as the system moves from the exit-channel barrier to the products was studied. Since properties associated with the rupturing C···H bond are similar for the C2H5(+) and C2H4F(+) exit-channel barriers, and integration of the C2H5(+) → C2H4 ± H reaction is approximately 2.5 times faster than the C2H4F(+) → C2H3F + H reaction, trajectories of the former reaction were propagated to gain insight into the exit-channel dynamics. Ensemble averaged results for C2H5(+) dissociation are well described by a model based on isotropic exit-channel dynamics which assumes that the product relative translational distribution arises from the centrifugal potential and relative translational energy distributions at the exit-channel barrier plus the exit-channel potential release. The width of the product translational energy distribution is sensitive to overall rotational angular momentum and its partitioning between C2H4···H(+) orbital angular momentum and C2H4 rotational angular momentum. The simulated product translational energy distribution for the C2H4F(+) → C2H3F + H reaction is broadened by relative translation-vibrational couplings in the exit-channel and is similar to the distribution used to fit crossed molecular beam data. Approximately 50% of the available energy is in product relative translation, which also agrees with experiment. RRKM calculations indicate that a second reaction mechanism, involving 1-2 hydrogen migration prior to C-···H bond fission, does not significantly contribute to C2H3F + H product formation.

Original languageEnglish
Pages (from-to)999-1011
Number of pages13
JournalPhysical Chemistry Chemical Physics
Issue number6
StatePublished - Mar 15 1999


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