Vibrational Relaxation in CO2 (1000)–CO2 Collisions

Abstract

The overall rate of vibrational relaxation of symmetric stretch-excited carbon dioxide, CO2 (1000), was measured in a new laboratory experiment. A perturbation–relaxation approach was used where the (1000) vibrational state of CO2 was populated via a temperature jump, and the rate of collisional energy exchange was monitored using transient diode laser absorption spectroscopy. The rate coefficient for the overall de-excitation of this state through collisions with carbon dioxide, which includes both vibrational–vibrational and vibrational–translational pathways, was determined to be (2.9 ± 0.3) × 10–11 cm3 s–1. This work provides new information about the efficiency of the vibrational–vibrational collisional energy exchange processes involving the (1000) state, which are expected to be significantly faster than the vibrational–translational process. These results should be useful for improving non-local thermodynamic equilibrium models for CO2-rich planetary atmospheres.