Velocity dependent state-to-state differential cross sections for rotational transfer in Li2–Xe using velocity selected double resonance

Abstract

We describe a new and wholly spectroscopic technique in which the state-to-state differential scattering cross section (dcs) is determined for rotationally inelastic atom–molecule collisions. The method uses two single frequency tunable dye lasers in a sub-Doppler double resonance experiment which has the added advantage that dependence on collision velocity may readily be determined. The method is illustrated by a determination of the dcs for rotational transfer (RT) in Li2 A 1Σ+u–Xe collisions. The dcs is obtained from the shape of the double resonance line and rotationally inelastic transitions Δj=−4 to +10 were studied. For each a range of initial relative velocities was selected and the scattering angles so obtained are differential in both angle and velocity. These are the first such measurements in atom–molecule scattering. The trends observed in scattering angle with Δj and with velocity are successfully interpreted using a hard ellipse model. We have observed significant differences in the dcs between upwards and downwards Δj transitions. The origins of these differences are discussed and emphasize the importance of the threshold velocity for a particular Δj channel.