Reactive and nonreactive charge transfer by the FMS method: low energy H++D2 and H+H2+ collisions

Abstract

The full multiple spawning (FMS) methodology for solving the time dependent Schrödinger equation for multiple electronic states is extended to reactive collisions on several electronic states. The computational complexity remains unchanged, less than double that of a quasiclassical trajectory computation. It is shown how the spawning approach can describe the bifurcation of the wave function into components exiting in different directions of space, as is the case when rearrangement of the atoms takes place. Low energy H⁺+D₂ and H+H₂⁺ collisions, which result in both reactive and nonreactive charge transfer are used as an illustration. The FMS method is used to generate converged opacity functions and cross sections even at higher energies when dissociation is energetically allowed. This suggests that also on a single potential energy function the FMS method offers a viable route to full dimensional reactive quantal scattering computations. For the H₃⁺ system, a diatomics in molecules (DIM) potential energy function is used in a diabatic basis where three electronic states are coupled. Comparison is made with the classical path approximation, the trajectory surface hopping method and stationary quantum mechanical scattering computations, which used the sudden approximation and the coupled states method. For the H⁺+D₂ collision, our results are close to those already published. The computations for the H+H₂⁺ collision, where the initial channel is an excited one, are distinctly different from the results of earlier, approximate, approaches.