Crossed beam studies of state-to-state vibrational energy transfer from the v=5 excited state of I2(X 1Σ+g) prepared by simulated emission pumping

Cross sections were measured as a function of kinetic energy E, for vibrationally inelastic collisions of He with I2(X 1∑+g) prepared in the v=5 excited state by stimulated emission pumping. The results for the transitions v=5→4 and v=5→6 are compared with those obtained previously for v=0→1 excitation of the ground state. Near threshold, the v=5→6 cross section displays a linear energy dependence, with a slope approximately 6 times that for v=0→1. The v=5→4 cross section has a finite intercept at E=0, and a slope approximately 5 times that for v=0→1. The scaling of the vibrationally inelastic cross sections with kinetic energy and quantum number can be understood semiquantitatively in terms of relationships derived from the forced harmonic oscillator model and microscopic reversibility.