Spectroscopic determination of the state-to-state differential cross section by velocity selected double resonance

We have measured the state-to-state differential scattering cross section (DCS) for a rotationally inelastic process using an entirely spectroscopic method. The system studied was ${\mathrm{Li}}_2$(${\mathit{A}}^1$ ${\mathrm{\Sigma }}_{\mathit{u}}^{+}$)-Xe and the method utilizes two color sub-Doppler double resonance. Analysis of the shape of the double resonance line yields the final distribution of relative velocity vectors. This represents the first measurement of a state-to-state DCS using thermal cell spectroscopy. In addition we have determined, also for the first time, the dependence of the state-to-state DCS on initial relative velocity. Results are presented for the Δj=6 rotationally inelastic process.