Product state distribution in time-dependent quantum wave packet calculation with an optical potential

We present a simple and efficient approach for extracting the final state-specific information in time-dependent quantum wave packet calculations for scattering or half-scattering problems without the artificial boundary reflection. The method, which is based on the compactness of the interaction picture wavefunction, employs an optical potential to absorb the flux of the Schrödinger picture wavefunction near the edge of the boundary. However, the absorption does not disturb the interaction picture wavefunction which is used to compute the stable product state distributions. Two numerical examples using this approach are given. One is for a model collinear photodissociation of CH₃I involving nonadiabatic coupling, and the other is for a rigid rotor scattered off a flat surface.