Rate constants for the CO2 0200-1000 relaxation

Abstract

An absorption-cell technique is utilized to determine the rate constants for the C${\mathrm{O}}_2$ ${02}^0$0-${10}^0$0 relaxation in C${\mathrm{O}}_2$ and binary-gas mixtures of C${\mathrm{O}}_2$-He and C${\mathrm{O}}_2$-${\mathrm{N}}_2$. The experiment consists of injecting a ∼2-nsec 10.4-μm pulse through the absorption cell—saturating the C${\mathrm{O}}_2$ ${10}^0$0 to ${00}^0$1 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 ${02}^0$0 and ${00}^0$1 states. The measured rate constants are $k_{\mathrm{C}{\mathrm{O}}_2-\mathrm{C}{\mathrm{O}}_2}=3\mathrm{}\pm 1$, $k_{\mathrm{C}{\mathrm{O}}_2-\mathrm{He}}=0.8\mathrm{}\pm 0.3$, and $k_{\mathrm{C}{\mathrm{O}}_2-{\mathrm{N}}_2}=3\mathrm{}\pm 1$, all in units of ${10}^5$ ${\sec }^{-1\mathrm{}}$ ${\mathrm{Torr}}^{-1\mathrm{}}$. 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 $k_{\mathrm{C}{\mathrm{O}}_2-\mathrm{C}{\mathrm{O}}_2}$ appreciably different from those measured.