Pulsed molecular beam study of state-to-state vibrational excitation in He+I2 collisions: Energy dependence of the <i>v</i>=0→1 cross section

Abstract

We report measurements of the kinetic energy dependence of the v=0→1 vibrational excitation cross section for He+12 collisions. These results were obtained with a new crossed, pulsed molecular beam apparatus having a variable molecular beam interaction angle and laser-induced fluorescence detection. The cross section shows a sharp onset at threshold, and rises nearly linearly with increasing energy to the highest experimental value of kinetic energy, about 13 times the vibrational quantum. At the higher energies, v=0→2 excitation is also observed. These data constitute the first measurements of the energy dependence of a microscopic state-to-state cross section for vibrational transitions in collisions of neutral species.