Do Semiclassical Trajectory Theories Provide an Accurate Picture of Radiationless Decay for Systems with Accessible Surface Crossings?

Abstract

We present quantum mechanical and semiclassical calculations of Feshbach funnel resonances that correspond to long-lived exciplexes in the A 2B2 state of NaH2. These exciplexes decay to the ground state, X 2A1, by a surface crossing in C2v geometry. The quantum mechanical lifetimes and the branching probabilities for competing decay mechanisms are computed for two different NaH2 potential energy matrices, and we explain the results in terms of features of the potential energy matrices. We compare the quantum mechanical calculations of the lifetimes and the average vibrational and rotational quantum numbers of the decay product, H2, to two kinds of semiclassical trajectory calculations: the trajectory surface hopping method and the Ehrenfest self-consistent potential method (also called the time-dependent self-consistent field method). The trajectory surface hopping calculations use Tully's fewest switches algorithm and two different prescriptions for adjusting the momentum during a hop. Both the adiabat...