Orbital alignment cross sections by stimulated emission probing : the state-to-state Ca Rydberg process Ca(4s17d^1D_2)+Xe->Ca(4s18p^1P_1)+Xe

The initial state alignment effect vs relative velocity is measured for a state-to-state Ca Rydberg collisional energy transfer process. The stimulated emission detection method is used to determine the alignment effect for the n,1-changing transition: Ca(4s17d1D2) + Xe -->Ca(4s18p1P1) + Xe+deltaE = -1.7cm-1. The rate of electronic energy transfer in this state-changing collision is observed to vary with the direction of the Rydberg electron charge cloud relative to the collision axis. Both the expected cos(4beta) and cos(2beta) dependencies are observed. The alignment data are analyzed to obtain the relative cross sections for the individual Ca(1D2) magnetic sublevels. The values of the m-sublevel cross sections sigma0 : sigma1 : sigma2 are 1.13+/-0.02:1.11+/-0.02:0.83+/-0.02. Qualitative interpretations of the relative cross sections in terms of both molecular (van der Waals) Born-Oppenheimer potentials and the impulse approximation are presented.