Near Infrared Absorption of Pure Carbon Dioxide up to 3100 bar and 500 K. I. Wavenumber Range 3200 cm-1 to 5600 cm-1

Near infrared absorption of pure CO in the v + v , 2v + v Fermi diad region around 3650 cm and in the 2v + v , v + 2v + v , 4v + v Fermi triad region around 5000 cm was measured at temperatures between 298 K and 500 K to a maximum pressure of 3100 bar. Density tuning of Fermi resonance is studied and compared with literature data on gaseous, liquid, and solid CO Band maximum positions determined within an extended temperature and density range indicate appreciable rotational freedom up to about the critical density (0.45 g · cm ) and repulsive interactions clearly coming into play above 0.9 g · cm . The vibrational intensity of the Fermi triad, up to about 1.0 g · cm is found to be independent of temperature and pressure within ± 2.5%, wich enables (pure) CO concentrations in a large region of states to be precisely and directly measured via quantitative high-pressure high-temperature near infrared spectroscopy.