Vibration relaxation time measurements via CRIIF (coherent Raman induced infrared fluorescence)

The population of an excited, totally symmetric state can be enhanced via a raman transition by exposing the sample simultaneously to a pumping frequency (ωL) and a Stokes frequency (ωS), such that (ωL−ωS) precisely matches the desired transition. Subsequent transfer of excitation to dipolar states, either inter- or intra- (v,v), can be detected from risetime and decay of infrared fluorescence. Thus, energy transfer probabilities from directly pumped, preselected states, whether these are totally symmetric or not, can be measured. An experimental configuration to test this concept was set up using an oscillator–amplifier single pulse ruby laser both for ωL and for pumping an infrared dye to generate ωS. Representative results were obtain for the D2/HCl system. The basic requirements for power, linewidth matching, and spacial superposition were analyzed. We conclude that our experiments demonstrated the feasibility of using CRIIF to measure v→v transfer rates from directly pumped totally symmetric states. There is a possibility that, for homoatomic molecules, sufficient populations of excited vibrational states could be generated to test their enhanced chemical reactivities.