Vibration–vibration energy-transfer kinetics monitored by thermal lens

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.