Ruth L. Robinson

Individual cross sections for 1D2 sublevels (ML=0, ±1, ±2) in the alignment-dependent process : Ca(4p2 1D2)+Rg→Ca(3d4p 1F3)+Rg as a function of rare gas

The Ca(4p2 1D2) state is prepared in a two‐step excitation with linearly polarized lasers. Two different angular wave functions are selected, Y2,0 or (Y2,−1−Y2,1)/, by using parallel or perpendicular laser polarizations, respectively. Subsequent collision with a rare gas atom (He, Ne, Ar, Kr, or Xe) populates the near‐resonant Ca(3d4p 1F3) state. The dependence of the collisional energy transfer process is measured as a function of the alignment of the initial 1D2 state wave function with respect to the average relative velocity vector. The laser‐selected Y2,0 and (Y2,−1−Y2,1)/ angular wave functions display dramatically different alignment dependences, which are understood by an analysis of the rotation properties of these wave functions. The relative contributions to the cross section of the individual 1D2 sublevels, ML=0, ±1, and ±2, are extracted, and these vary considerably depending on the rare gas. For He, the ML=±2 sublevel (asymptotic Δ molecular state) contributes the most to the total cross sec...

Alignment effects involving multiple pathways. Electronic energy transfer of Sr 5s6p 1P1 with rare gases

Orbital alignment effects and branching fractions have been measured for collisionally induced electronic energy transfer from the Sr 5s6p 1P1 state to seven near-resonant states : 5s6p 3P2,1,0, 4d5p 1D2 and 4d5p 3F4,3,2. The measurements were carried out in a crossed-beam experiment using a pulsed, linearly polarized laser which propagates perpendicular to the initial average relative velocity vector of the collision partners. The results show remarkably high specificity in both the formation of product states and the alignment effects into each state. With He as a collision partner, formation of the 3F3 state shows a preference for the laser polarization parallel to the collision axis; formation of the 3P1 state shows no alignment dependence, whereas the 3P0 state shows a strong preference (4 : 1) for the perpendicular polarization. All other states are preferentially formed with the perpendicular laser polarization. In addition, the branching fractions produced by collisions with He are highly non-statistical. With Xe, the branching fractions approach those of a statistical distribution, suggesting a strong interaction; however, alignment preferences are still discernible for individual states. Despite the complexity and large number of curve-crossing possibilities in this multistate system, several highly selective crossings are inferred from the observed alignment effects. Specific alignment preferences are discussed in terms of symmetry and energy considerations.