The question of energy randomization in the decomposition of chemically activated C2H4F

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Abstract
The question of whether energy randomization occurs in the decomposition of chemically activated C2H4F is further examined with the crossed molecular beam technique by measuring the collision energy dependence of the C2H3F product recoil energy distributions for the reaction F+C2H4. The symmetric angular distributions of product molecules indicate that the lifetime of C2H4F remains longer than a rotational period even at the highest collision energy studied. The effect of the exit channel barrier becomes less important at higher collision energies since the fraction of the total energy associated with the barrier becomes smaller as the collision energy increases. The experimental recoil velocity distributions yield average product translational energies which remain almost constant at ∼50% of the total available energy: These results are shown to be inconsistent with phase space theory and the recent ’’Tight Transition State’’ theory of Marcus. Our experiments and the infrared chemiluminescence experiments of McDonald and co-workers indicate that the C2H3F product energy distribution is nonstatistical, a conclusion seemingly at variance with Rowland’s determination of lifetimes from stabilization of chemically activated C2H4F produced in hot-atom experiments. We discuss possible explanations for differences among the experimental data on this system.