A fast Fourier transform method for quasiclassical selection of initial coordinates and momenta for rotating diatoms

This paper describes a new fast Fourier transform technique to determine the transformations from action-angle variables to Cartesian coordinates for a rotating diatomic molecule. This allows one to obtain the initial values of the coordinates and momenta for a given v and J from properly weighted radial and angular distributions as required in quasiclassical trajectory calculations. This method offers a number of advantages over previous methods for obtaining initial values. It is very accurate, even for cases of high J. This method works equally well for all types of diatomic potentials. Results are reported for Morse potentials and extended Rydberg potentials.