INVESTIGATION OF LIBRATIONAL MOTIONS IN GAS-PHASE CO2 CLUSTERS BY COHERENT RAMAN-SPECTROSCOPY

Coherent Stokes Raman scattering (CSRS) has been employed to investigate the spectroscopy of large CO2 clusters formed in the expansion of a supersonic jet. In the low-frequency range, around 72 and 88 cm-1, the cluster spectrum features two peaks which can be assigned to the excitation of librational modes. With progressive expansion, i.e. decreasing internal temperature, these peaks shift towards larger wave numbers. Comparison with the data obtained in solid CO2 shows that the cluster librations are in thermal near-equilibrium with the monomer rotations. © 1990.