Stochastic theory for molecular collisions in the perturbation limit

Previous stochastic theory research has described individual molecular collisions by a master equation or a Fokker-Planck equation. The perturbation (weak coupling) limit of this theory is examined more carefully in this paper. It is shown how the formulation reduces to exact quantum mechanics in the perturbation regime. The methods are applied to the collinear forced quantum oscillator model for purposes of comparison with other theories. The results of this work and previous research show that stochastic collision theory firmly connects up to both the weak and strong coupling limits. It is suggestive that computationally attractive schemes which afford reasonable accuracy can now be developed for the intermediate coupling regime as well.