Semiclassical transition state theory for nonseparable systems: Application to the collinear H+H2 reaction

Two different kinds of semiclassical approximations are used to evaluate a previously obtained quantum mechanical transition state theory rate expression. No assumptions, however, such as separability of the Hamiltonian, vibrationally adiabatic motion along a reaction coordinate, etc., are incorporated. Application is made to the collinear H+H2 reaction, and agreement with accurate quantum scattering calculations is found to be reasonably good. The results indicate that transition state theory: provided no assumptions of separability are included: is probably as accurate quantum mechanically as it has been found to be classically for describing the threshold of chemical reactions with an activation barrier