An experimental exploration of the energy gap law for vibration-translation energy transfer. The I₂ * + M system

New crossed beam inelastic scattering data have been obtained for the I2(B 0u+)(v′=35) + M system where M = He, Ne, or Ar. The data are used to explore exponential energy gap law (EGL) scaling for vibration-translation (V-T) energy transfer over a range of collision dynamics and interaction potentials. Relative cross sections for Δv changes in the vibrationally (and rotationally) inelastic scattering were obtained with center-of-mass collision energies (Ec.m.) of 350 and 1500 cm-1 for He, 1370 cm-1 for Ne, and 2050 cm-1 for Ar. When these experiments are combined with earlier beam and 300 K bulb experiments plus a classical trajectory calculation, the collisions range from nearly impulsive to nearly adiabatic and encompass Ec.m. distributions ranging from 300 K thermal to narrow crossed beam Gaussians. The trajectory calculations simulate monochromatic Ec.m. collisions. The various interaction potentials include both minimal and substantial attractive contributions. EGL scaling is a good representation of the V-T transition probabilities over all of these conditions. © 1991 American Chemical Society.