State-Resolved Differential Cross Sections for Rotational Transitions inNa2+Ne (He) Collisions

We demonstrate a new technique for the measurement of state-resolved differential cross sections for elastic and inelastic collision processes involving molecules with small level spacing. Lasers are used to label a specific rovibronic level by modulation of its population via optical pumping and to probe the population of neighboring levels by laser-induced fluorescence. First results on ${\mathrm{Na}}_2$ + Ne (He) collisions show that beyond the center-of-mass scattering angle ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=50\mathrm{}°$ nearly all collision events are inelastic.