Carbon Monoxide: Spectroscopic Characterization of the High–Pressure Polymerized Phase

Abstract

Solid carbon monoxide transforms to the δ–phase at about 48 kbar at room temperature. In this pressure regime (50 kbar and greater), carbon monoxide undergoes a transformation at room temperature to a light–pink solid, which has not been studied in detail and may be different from the δ–phase. Exposure to moderate light intensities at these P–T conditions converts the system to a dark red material. We report visible and infrared absorption as well as Raman investigations of this dark red substance, which likely contains a polymeric product of the photochemical reaction. This material is stable upon pressure release down to ambient conditions. Previous studies speculated that the dark red product was a mixture of poly–carbonsuboxide (C₃O₂) and oxalic anhydride (C₂O₃). In contrast, we present evidence that this material is composed of graphitic–like carbon, carbon dioxide, and possibly a polymerized network containing $- \left( {{\text{C = O}}} \right) - {\text{O}} - \left( {{\text{C}} - } \right) = {\text{C}} <$ as a repeating unit.