Collision-Induced Fine-Structure Transitions of Hg(63P1 → 63P0) with N2 and CO. 1. Initial Orbital Alignment Effects

Abstract

Effects of initial orbital alignment have been investigated for the fine-structure transitions of Hg(63P1 → 63P0) induced by collisions with N2 and CO in a crossed molecular beam experiment using a laser pump−probe technique. The orbital alignment effects are observed by monitoring the population of the product Hg(63P0) as a function of polarization angle (θ) of the linearly polarized pump laser, which prepares the Hg(63P1), relative to the direction of the initial relative velocity vector. The alignment effects in this study are represented by an asymmetry parameter β in the angle-dependent cross section, σ(θ) = σ0[1 + βP2(cos θ)]. The measurement for Hg−N2 exhibits a large alignment effect with β = −0.50(7), but for Hg−CO a small effect with β = −0.20(6). Both processes show preference for perpendicular excitation of the pump laser with θ = 90°. The nonadiabatic transitions responsible for this fine-structure process therefore occur mainly via the B̃(23A‘ + 23A‘ ‘) molecular electronic state and not via the Ã(13A‘) state for Hg−N2. In contrast, the small effect for Hg−CO indicates that the contribution from the nonadiabatic transition via the à state is comparable with that via the B̃ state for Hg−CO.