Quasiclassical model for resonance widths in quantal collinear reactive scattering

A quasiclassical model with no adjustable parameters is proposed for analysis of resonance widths of collinear atom--diatom reactions. We find two important contributions to the widths. One comes from tunneling through adiabatic exit channel barriers. The other involves the stability frequency of resonant periodic orbits. This frequency, if it is imaginary, is a measure of the nonadiabatic coupling in the system. We find that the resonances of the H+HH exchange reaction are determined by this nonadiabatic coupling. The higher lying resonances of the H+MuH system are controlled by the tunneling mechanism. We find that the resonant periodic orbit of the HMuH reaction is stable over a large energy range. The implications of this stability on analysis of quantal computations are discussed in detail