THEORETICAL-STUDY OF CA(4S5P P-1)-]CA(4S5P P-3) ENERGY-TRANSFER IN COLLISIONS WITH HE - INITIAL AND FINAL-STATE ALIGNMENT

In this paper we present the results of close-coupling calculations of the cross sections for Ca(4s5p P-1)-->Ca(4s5p P-3) energy transfer in collisions with He, based on new potential energy curves. Particular attention is devoted to the simulation of the recent experiment of Smith and co-workers [J. Chem. Phys. 96, 8212 (1992)], in which, for the P-1-->P-3(2) transfer both initial and final alignment are controlled with respect to the initial relative velocity vector of the two partners V-rel. The calculated polarization ratios (sigma(perpendicular to)/sigma(parallel to)), defined as the ratio of the cross sections for the P-1-->P-3 transfer summed over final levels for initial alignment of the 5p orbital perpendicular and parallel to V-rel are in good agreement with the experimental results. The theoretical cross sections for the P-1-->P-3(2) transfer determined in the so-called collision frame (sigma(j1m1m1-->j2m2m2)), where the axis of quantization is taken along V-rel are in good agreement with the experiment in the case of initial perpendicular excitation, but show quantitative and qualitative disagreement in the case of initial parallel excitation. We find that relative populations into the final m(2) levels depend strongly on the initial orientation of the 5p orbital with respect to the initial collision plane. However, we show, that in the case where the 5p orbital lies in the initial collision plane, the relative populations in the final m(2) components of the P-3(2) state depend exclusively on interactions among the exit channels.