Rate constants for the CO2 020--1000 relaxation

An absorption-cell technique is utilized to determine the rate constants for the CO2 0200-1000 relaxation in CO2 and binary-gas mixtures of CO2-He and CO2-N2. The experiment consists of injecting an approximately 2-nsec 10.4-μm pulse through the absorption cell--saturating the CO2 1000 to 0001 transition, and monitoring the subsequent molecular re-equilibrations by recording the temporal intensity of a spatially overlapping probe beam in the 9.4-μm band connecting the 0200 and 0001 states. The measured rate constants are k/sub CO2-CO2/ = 3 +- 1, k/sub CO2-He/ = 0.8 +- 0.3, and k/sub CO2-N2/ = 3 +- 1, all in units of 105 sec-1 Torr-1. The experimental approach also yields information on the thermalization of other processes having slower rates, and these are discussed qualitatively. Finally, a comparison is made with other related experimental investigations and two calculations which predict values for k/sub CO2-CO2/ appreciably different from those measured. (5 figs., 16 refs.)