The calculation of kinetic isotope effects based on a single reaction path

In this paper we propose a new method for calculating kinetic isotope effects without calculating a separate reaction path for each isotopically substituted species. The new method yields reasonable kinetic isotope effects from calculations using the same reaction path for all isotopic variations. The method is tested by carrying out variational transition state theory calculations, including multidimensional tunneling contributions, for the reactions OH+H-2-->H2O+H, CH3+H-2-->CH4 +H, and H+H-2-->H-2+H and nine deuterium-substituted isotopologs of these reactions. The results are very encouraging. (C) 1998 American Institute of Physics. [S0021-9606(98)01139-8].