High-pressure UV spectroscopy on oxygen up to 1.5 GPa

UV absorption spectra of molecular oxygen were measured at pressure up to 1.5 GPa and temperature between 17 and 297 K. In the supercritical phase, an absorption band was observed in a UV region between 4.5 and 7 eV and showed an appreciable enhancement in the intensity with pressure. The absorption cross-section, σeff, of the UV band at 1.5 GPa, estimated from the molar volume obtained by present X-ray diffraction experiments, reached three orders of magnitude of previous one measured at 1.0 MPa. The observed UV absorption of high-density oxygen was attributed to the two-molecule process by an antiferromagnetic O2 pair.