Substantial velocity dependence of rotationally inelastic collision cross sections in Li2—Xe

A Doppler-based velocity selection technique has been used to measure the relative velocity dependence of the cross sections σ_ji,Δ(ν_r) for rotationally inelastic collisions from level j_i to j_i + Δν₁ = 8,22,42) in ⁷Li^*₂ A ¹Σ⁺_u)—Xe. The σ_jν^±2(ν_r) are strongly attenuated at a smaller ν_r by “torque averaging” due to molecular rotation; in contrast, for large |Δ|, σ_jiΔ = ν_r⁻ⁿ (1 n 2). An empirical intermolecular potential which reproduces these types of behavior for 3-D classical trajectories is exhibited.