Normal and resonance Raman spectra of gaseous chlorine excited with an argon ion laser

Normal and resonance Raman effects in gaseous chlorine were carefully studied with a powerful argon ion laser. No resonance Raman behaviour could be detected in the spectra excited by visible laser lines with wavelengths down to 4545A. The fine structures of the normal Raman spectra were examined. Resonance Raman spectra were obtained with the 3638 and 3511 A UV line excitation. Progressions with seven overtones were recorded. The fine structures in each overtone region were analysed and assigned as the Q and S band heads of various isotopic molecules. The Raman cross-section was enhanced only by a factor of 1.3 in the resonance case and the integrated intensity of each overtone was about one-third of that of the fundamental. Those two characteristics indicate that the resonance Raman term in gaseous chlorine is small in comparison with the normal Raman term even when the energy of the excitation laser line is 7593 cm−1 above the dissociation limit.