Theoretical study of Ca(4 s 5 p  1 P )→Ca(4 s 5 p  3 P ) 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 1P)→Ca(4s5p 3P) 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 1P→3P2 transfer both initial and final alignment are controlled with respect to the initial relative velocity vector of the two partners Vrel. The calculated polarization ratios (σ⊥/σ∥), defined as the ratio of the cross sections for the 1P→3P transfer summed over final levels for initial alignment of the 5p orbital perpendicular and parallel to Vrel are in good agreement with the experimental results. The theoretical cross sections for the 1P→3P2 transfer determined in the so-called collision frame (σj1m1m1→j2m2m2), where the axis of quantization is taken along Vrel 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 m2 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 m2 components of the 3P2 state depend exclusively on interactions among the exit channels.