First and Second Overtone Absorption of Pure Carbon Monoxide to High Pressures and Temperatures

The first and second overtone absorption of pure carbon monoxide was measured at supercritical temperatures between 293 K and 500 K in an extended pressure range up to 2.8 kbar. The near infrared bandshape, almost up to the critical density, is adequately represented by summing up over individual rotation-vibration lines with half-widths proportional to density. Band maximum positions and vibrational intensities between gaseous and liquid-like states are reported and discussed. The molar integrated absorptivity is independent of temperature and, in the first overtone, varies by less than 2% with density which enables direct and precise measurements of CO concentrations in fluid phase equilibria and reactions via high-pressure near infrared Spectroscopy.