Lattice phonons of solid phases (α,β,δ,ε) of carbon monoxide by optical studies

The phase diagram of solid carbon monoxide was investigated in the pressure range 0–10GPa and temperature range 30–300K by infrared and Raman spectroscopy. The tentative phase diagram known from the literature was expanded and specified in detail. The δ-phase region is divided into two subphases—δrot and δloc—similar to solid nitrogen. The pressure-temperature behavior of the elementary and combined excitations was also followed up. The vibron overtone region was carefully investigated by FTIR spectroscopy as a function of temperature at different pressures; the fundamental region was investigated by Raman spectroscopy. The features of the IR-active phonon sideband to the vibron overtone were investigated in detail in the entire pressure-temperature region. The lattice-phonon spectra were studied by Raman spectroscopy as a function of pressure (at lowest temperature) and by IR spectroscopy as a function of temperature at saturated vapor pressure.