High-pressure Raman scattering experiments of O-2 and N-2 were carried out at 296 K and at pressures up to 10 and 6 GPa, respectively, and the pressure dependence of vibrational spectra Of O-2 was studied on the basis of molecular interactions in comparison with N-2. An appreciable contribution of the attractive interaction to the vibrational frequency was observed for fluid O-2. The linewidth of the spectra for fluid O-2 showed a sharp increase with increasing pressure, and the fluid-solid transition was observed at 5.9 GPa with a sudden drop of the linewidth. (C) 2004 Elsevier B.V. All rights reserved.