The Raman scattering of solid carbon monoxide was studied in a diamond cell from 15 to 297 K at pressures from 1.0 to 5.8 GPa. At low temperature a transition occurs near 3.4 GPa from the known a-phase (space group P&3) to a new e-phase (structure unknown), rather than to the predicted y-phase (P42/mnm). A transformation from /3-CO (space group P63/mmc) into a new &phase (Pm3n?) was found near 5.2 GPa at room temperature. Above about 4.6 GPa and 80 K, CO reacts photochemically when irradiated with visible laser light. The photoreactivity may be associated with the formation of a yellow polymer, which can be recovered at zero pressure.
-Nous avons déterminé le diagramme de phase du monoxyde de carbone par diffraction des rayons X et spectroscople Raroan, de 15 â 297 K et i des pressions de 1.0 â 10.0 GPa. A basse température et au voisinage de 3.4 GPa, la phase connue a (groupe d'espace P2]3) se transforme en une phase nouvelle G (de structure Inconnue), au lieu de la phase prévue t (PAj/renra). Nous avons trouvé une transformation de C0-$ (groupe d'espace P&3/ramc) en une phase nouvelle i (Pm3n), au voisinage de 5.2 GPa, à la température ambiante. Au-dessus de 4.6 GPa et 80 K, environ, lorsque Irradié par lumière visible laser, C0 subit une réaction photochimique. Cette tendance à réagir peut être associée avec la formation d'un polymère jaune qui subsiste jusqu' à" pression nulle. Des mesures ESCA Indiquent que le polymère est composé de sous-oxyde de carbone ^(^x-Abstract-The phase diagram of solid carbon monoxide was determined by x-ray diffraction and Raman spectroscopy from 15 to 297 K at pressures from 1.0 to 10.0 GPa. At low temperature a transition occurs near 3.4 GPa from the known a-phase (space group P2i3) to a new c-phase (structure unknown), rather than to the predicted ir-phase (P42/mnm). A transformation from p-CO (space group P63/mmc) Into a new 4-phase (Pm3ti) was found near 5.2 GPa at room temperature. Above about 4.6 GPa and 80 K, CO reacts photochemically when irradiated with visible laser light. The photoreactlvlty may be associated with the formation of a yellow polymer, which can be recovered at zero pressure. ESCA measurements Indicate that the polymer Is composed of carbon suboxide (C3Q2)x* I.
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