Absolute infrared intensities and band shapes in pure solid CO and CO in some solid matrices

Abstract

The infrared absorption spectra of carbon monoxide in argon matrices have been studied over a wide range of CO concentrations. The absolute infrared intensities of pure crystalline CO and of CO in argon matrices have been measured. The technique of using the second moment to determine the baseline of the absorption band has been tested and found to improve the data. The absolute integrated molar absorption coefficient of pure solid CO was found to be A=58.1±5.50 km mol⁻¹ (1 km/mole=100 cm/mmole) and that for CO in the argon matrices is 66.5±2.4 km mol⁻¹. The two values are believed to be the same within experimental error. Studies were also made of CO trapped in different matrices, including SF₆, C₆H₆, and CCl₄. The absolute intensity of CO increases from the gas phase (A=58.0 km mole⁻¹) to the pure solid phase (A=58.1) or to the solid matrices (66.5−114 km mol⁻¹, depending on the matrix) apparently due for the most part to the electric field effect. The band shapes have been analyzed to obtain the second and fourth moments and hence the intermolecular torques and dipole time−correlation functions. The large values for the torques and slow decay of the correlation function with time from one system to another suggest that the CO molecules have either greatly hindered rotation or no rotation at all in the pure solid and in the solid matrices.