Vibration–vibration energy-transfer kinetics monitored by thermal lens

Abstract

The time development of the thermal-lens signal from CO₂ at various pressures has been measured and interpreted. The waveforms obtained are found to be very sensitive measures of the rate constants for individual energy-transfer steps and comparison of theory with experiment has allowed the determination of rate constants for the processes CO₂(001)→ CO₂(030), k=(10.22 ± 0.7)× 10^–15 molecule^–1 cm³ s^–1 and CO₂(010)→ CO₂(000), k= 7.9 × 10^–15 molecule^–1 cm³ s^–1. The process CO₂(001)→ CO₂(040) is shown to be relatively insignificant and it is also shown that it is not necessary to postulate a specifically endothermic step in the mechanism to explain the transient cooling of pure CO₂.