Collision-induced fine-structure transitions of Hg(6(3)P(1)-> 6(3)P(0)) with N-2 and CO. 1. Initial orbital alignment effects

Effects of initial orbital alignment have been investigated for the fine-st ructure transitions of Hg(6(3)P(1) --> 6(3)P(0)) induced by collisions with N-2 and CO in a crossed molecular beam experiment using a laser pump-probe technique. The orbital alignment effects are observed by monitoring the po pulation of the product Hg(6(3)P(0)) as a function of polarization angle (t heta) of the linearly polarized pump laser, which prepares the Hg(6(3)P(1)) , relative to the direction of the initial relative velocity vector. The al ignment effects in this study are represented by an asymmetry parameter bet a in the angle-dependent cross section, sigma(theta) = sigma(0)[1 + beta P- 2(cos theta)]. The measurement for Hg-N-2 exhibits a large alignment effect with beta = -0.50(7), but for Hg-CO a small effect with beta = -0.20(6). B oth processes show preference for perpendicular excitation of the pump lase r with theta = 90 degrees. The nonadiabatic transitions responsible for thi s fine-structure process therefore occur mainly via the (B) over tilde(2(3) A' + 2(3)A ") molecular electronic state and not via the (A) over tilde(1(3 )A') state for Hg-N-2. In contrast, the small effect for Hg-CO indicates th at the contribution from the nonadiabatic transition via the A state is com parable with that via the (B) over tilde state for Hg-CO.