Rotational and vibrational relaxation of the ν1/2ν2 Fermi dyad in CO2 gas from Raman-infrared double resonance experiments

Abstract

Time-resolved Raman-infrared double resonance experiments have been conducted on CO2 gas in order to determine collisional relaxation rates of energy levels. These total depopulation constants are measured in a three-level double resonance scheme. A pulsed Raman excitation populates the studied state over a brief time interval (7 ns). The ensuing collisional depopulation of this level is monitored by a continuous probe CO2 laser whose transition originates in the same level. The transient absorption on the probe laser gives the time dependent population behavior. The high selectivity of the lasers allows the study of vibrational and rotational levels. The relaxation rates, of the (1000) vibrational state and, for the first time, of the J=14–34 rotational levels of the (0200) vibrational state, have been measured. The derived broadening coefficients have been compared to those calculated by a semiclassical model.