Knowledge Bank

A new crossed molecular beam experiment is based on electronic fluorescence spectroscopy after laser pumping of selected ro-vibrational levels in excited states. The spectroscopy provides relative cross sections for single-collision rotationally and vibrationally inelastic scattering to specific final states with close control over collision energies. Experiments that involve collisions of $B3=0+uI2$ (initial $v\prime =15$ or 25 or 35) and collision partners such as He show all possible $\Delta v$ changes with the amount of energy transferred approaching the collision energy. The relative cross sections are in fair correspondence to classical trajectory calculations. The total cross sections for vibrationally inelastic scattering is large, being entirely competitive with that for rotationally inelastic scattering. Scattering from several initial levels in $S1$ glyoxal also show relatively large cross sections. In this case there is high selectivity among the glyoxal modes that can participate in the energy transfer. Cross sections for excitation of rotations and of the glyoxal torsion $(\nu 7)$ depend primarily on $\Delta E$ without distinguishing between rotational or vibrational excitation.