High-pressure and low-temperature infrared study of solid oxygen: Evidenceof a new crystal structure

Infrared spectroscopy has been applied to the study of solid oxygen at high pressure and low temperature. An absorption line in the vibron fundamental mode region has been observed, and its behavior with pressure measured up to the transition to the epsilon phase. This absorption, not expected accor ding to the symmetry of the delta phase, indicates the existence of a new c rystal structure between 2 and 8 GPa at low temperature. The comparison of the infrared and Raman frequency evolution with pressure is done quantitati vely on the basis of a simple vibrational coupling model and the intermolec ular coupling force constant is obtained. In contrast to solid hydrogen, he re the coupling constant is positive and shows a strong dependence on the i ntermolecular distance which can indicate that significant charge transfer processes are already present in this low-pressure phase. [S0163-1829(99)05 533-2].