DIODE-LASER STUDIES OF COLLISIONAL ENERGY-TRANSFER

Time-resolved infrared diode laser absorption spectroscopy has proven to be a remarkably sensitive probe for the study of collisional energy transfer processes. The high spectral resolution makes it possible to determine the rovibrational states, as well as the translational ener gy content, of small molecules excited in collisions. We illustrate th is technique with studies of ''hot'' atom collisions and show that in the case of H + CO2 encounters the experimental results can be explain ed by a simple ''breathing ellipsoid'' model. Recently, we applied dio de laser spectroscopy to studies of collisional energy transfer from h ighly vibrationally excited molecules, containing chemically interesti ng amounts of energy. Our results indicate that most of the energy los s from the donor molecule results in rotational and translational, rat her than vibrational, excitation of the ''bath'' gas species. The smal l number of collision events which lead to vibrational excitation of t he bath molecule states appears to be dominated by long-range forces i n which donor vibrational energy is exchanged for acceptor vibrational energy with little or no excitation of the rotational and translation al degrees of freedom.