Dynamics of electronically inelastic collisions from 3D Doppler measurements

Flux-velocity contour maps were obtained for the inelastic collision process Ba${(}^1$ ${\mathit{P}}_1$)+${\mathrm{O}}_2$ ${\mathrm{N}}_2$→Ba${(}^3$ ${\mathit{P}}_2$)+${\mathrm{O}}_2$ ${\mathrm{N}}_2$ from Doppler scans of scattered Ba${(}^3$ ${\mathit{P}}_2$) taken over a range of probe laser directions in a crossed-beam experiment. Collision with ${\mathrm{O}}_2$ resulted in sharply forward scattered Ba${(}^3$ ${\mathit{P}}_2$), with efficient conversion of inital electronic energy into ${\mathrm{O}}_2$ internal energy and little momentum transfer. Collision with ${\mathrm{N}}_2$ was dominated by wide-angle scattering with most of the available electronic energy appearing in product translation. The results suggest the importance of large-impact-parameter collisions and a near-resonant energy transfer in the case of ${\mathrm{O}}_2$, while for ${\mathrm{N}}_2$ close collisions dominate despite the presence of an analogous near-resonant channel. The results represent the first direct experimental demonstration of a near-resonant quenching process.