Velocity-Selective Double Resonance: A Novel Technique for Determining Differential Scattering Cross Sections

The relationship between the velocity vectors of a gas-phase molecule before and after a collision is given by the differential cross section. Optical-optical double-resonance experiments using highly coherent sources can be used to obtain this information. Predictions and experimental considerations are discussed, and data are presented for elastic scattering in the $\upsilon =18\mathrm{}$, $j=13\mathrm{}$ level of $A{}_{}{}^1{}_{}{}^{}\Sigma _{\mathrm{u}}^{}{}_{}{}^{+}$-state ${\mathrm{Li}}_2$ by Xe atoms.