A photoacoustic study of intramolecular energy transfer in CO2 deactivated by monatomic gases between 153 and 393 K

Abstract

Rates of (V–V) vibrational energy transfer from the CO2 (0001) level to the levels of the bending (b) and symmetric (s) stretching modes and from these two modes to translation–rotation (V–T) are measured for CO2 deactivated by monatomic gases between 153 and 393 K by a photoacoustic method. This technique is complementary to experiments involving fluorescence quenching or ultrasonic dispersion and makes possible a better analysis of the details of vibrational exchange processes. In the temperature range under study the variation in the (V–T) rate constants appears to be considerably less than semiclassical theories might lead us to believe even if attractive forces are accounted for. The hypothesis in favor of transfer to the rotation of CO2 at low temperatures permits a better approach to experimental results, but nevertheless remains insufficient. For the cases of deactivation by all the inert gases except helium, the experimental results lead to retaining three dominant (V–V) transfer processes: (0001) → (2000), (0001) → (1110) and (0001) → (1000). In the case of neon the last of these three processes is the most important above 350 K. Shin’s theory shows that this result is consistent with fluorescence measurements which go up to temperatures as high as 800 K. Below 250 K the measured rates of both (V–V) and (V–T) transfers change more slowly with temperature than those calculated.