Dynamics calculations for the Cl+C2H6 abstraction reaction:: Thermal rate constants and kinetic isotope effects

Thermal rate constants and H/D kinetic isotope effects for the Cl+C2H6-->HCl+C2H5 reaction were computed by microcanonical variational transition state theory on a high-level ab initio potential energy surface (PES). The calculations show that the reaction proceeds through a "loose" transition state, and so the consideration of variational effects is important. The PES presents a van der Waals minimum in the products side. The calculations indicate that this minimum has no effect in the forward reaction and little effect in the reverse reaction for temperatures above room temperature. The analysis of the kinetic isotope effects shows that the contribution due to tunneling is fairly small, but with an important role played by the variational effects. Classical trajectory calculations were also performed on a semiempirical PES, which was parametrized from own ab initio calculations. This method was utilized to compare the HCl relative velocity distribution with those obtained experimentally. The results show a good agreement with experiment and reinforce the reliability of the proposed mechanism for this reaction. (C) 2003 American Institute of Physics.