A mixed quantum-classical method for calculating product energy partitioning based on a reaction path Hamiltonian is presented and applied to HF elimination from fluoroethane. The goal is to describe the effect of the potential energy release on the product energies using a simple model of quantized transverse vibrational modes coupled to a classical reaction path via the path curvature. Calculations of the minimum energy path were done at the B3LYP/6-311++G(2d,2p) and MP2/6-311++G** levels of theory, followed by energy-partitioning dynamics calculations. The results for the final HF vibrational state distribution were found to be in good qualitative agreement with both experimental studies and quasiclassical trajectory simulations.

The dynamics of four-centered HCl elimination from chloroethane are studied using a mixed quantum-classical method based on a reaction path Hamiltonian. Both the structural details of the reaction and the partitioning of the exit-channel potential energy to the products are analyzed. The minimum energy path was calculated at the B3LYP/6-311++G(2d,2p) level of theory, which was followed by energy-partitioning dynamics computations. Selective vibrational excitation of the HCl product was observed, leading to a vibrational state distribution in good agreement with experiment. Differences between HCl elimination from C(2)H(5)Cl and HF elimination from C(2)H(5)F, particularly in the ethylene fragment, were observed and are discussed.