M-preserving propensities for rotationally inelastic NH3-He collisions. In the kinematic apse frame

Abstract

Abstract Semiclassical calculations are used to obtain integral cross sections in both the initial velocity, or collision-fixed, frame and the kinematic apse frame (defined by Khare et al.) for rotational excitation in the NH 3 -He system at a collision energy of 100 cm − . A comparison with earlier close-coupling calculations in the initial velocity frame. using the same interaction potential, shows that the semiclassical method predicts relative M -dependence quite accurately. The kinematic apse cross sections, unlike those in the initial velocity frame, are highly diagonal in the quantum number M . An examination of the M -dependent transition probabilities as a function of impact parameter indicates that the propensity for conservation of M in the kinematic apse frame is due to the dominance of backward, or high-angle, scattering in the cross section. The propensity for conservation of M breaks down for large impact parameters where the interaction is attractive.