Generalized path integral based quantum transition state theory

A theory for calculating rates of transitions in quantum systems is presented and applied to desorption of H2 from a Cu(110) surface. The quantum transition state is defined as a conical dividing surface in the space of closed Feynman paths and a ‘reaction coordinate’ in this extended space is used to parametrize a reversible work evaluation of the free energy barrier. In a low temperature, harmonic limit the theory reduces to instanton theory. Above the cross-over temperature for tunneling, the theory reduces to the centroid density approximation and in the callsical limit, variational classical transition state theory is recovered.