NEAR-RESONANT VIBRATIONAL ENERGY TRANSFER AMONG ISOTOPES OF CO2

Quantitative calculations are presented which show that large (approximately gas kinetic) cross sections observed for vibrational-vibrational energy transfer between isotopes of CO2 are due to long-range forces. The mechanism involved in the transfer of a quantum of asymmetric stretch vibration from C12O216 to C12O216 and O16C12O18 can be described in terms of dipole-dipole coupling. However, dipole-dipole coupling is too weak to describe the energy transfer to C13O216. It is shown that in this case dipole-octupole coupling is expected to be stronger than dipole-dipole coupling. The room-temperature results are reproduced by assuming a value of 1 × 10-67 stat C2 cm6 for the square of matrix element for the vibrational transition. Temperature dependence of the rate constant is calculated to put this hypothesis to test. © 1969 The American Physical Society.