State-to-state vibrational and rotational energy transfer in CO2 gas from time-resolved raman-infrared double resonance experiments

Abstract

A time-resolved Raman–infrared double resonance technique was used to study collisional relaxation rates of vibrational and rotational energy levels in CO2 gas at 295 K. A pulsed Raman excitation populated a selected rovibrational initial state. Measurements of the rates of transfer from the pumped initial state into specific final states were carried out using time-resolved laser absorption spectroscopy. First, the transfer rates were determined for the five lower vibrational energy levels. In particular, it was confirmed that the rate of transfer between the two Fermi levels (1000) and (0200) is very small [(5.3±0.2)×104 Torr-1 s-1]. The rotational structure inside the (0200) vibrational level was also studied. A kinetic master equation was used to model energy transfer among rotational levels. The state-to-state rotational energy transfer rates were calculated by the fitting and scaling laws. The ability of different laws (ECS-P, ECS-EP, MEG) was then compared in order to reproduce the time-dependent population evolution. © 1998 John Wiley & Sons, Ltd.