OPTOACOUSTIC STUDY OF THE INFRARED MULTI-PHOTON EXCITATION OF ETHYLENE

The optoacoustic effect was used to detect the infrared multiphoton excitation of ethylene as a function of laser wave length and laser energy fluence. The strong absorptions were observed at 949 cm-1, 953 cm-1 and 939 cm-1. The dependence of the energy absorption on the laser energy fluence shows that the absorption at 949 cm-1 is due to the resonance of the single quantum transition whereas the absorptions at 953 cm-1 and 939 cm-1 are due to the resonance of the double quantum transitions. The energy shift of the later transitions was explained in terms of Fermi resonance of the overtones of v7 and v8 modes. The onset of highly multiple quantum transitions were observed at high laser energy fluence. © 1979.