MOMENT ANALYSIS OF INFRARED SPECTRA

The method of moment $analysis^{1}$ is used to interpret the band shapes of some infrared $spectra^{2-4}$ of CO in gaseous, liquid and solid pure phases and mixtures. The first moment determines the frequency shift. The third and fourth moments are used to obtain values of the mean squared torque on a CO molecule. In gaseous CO and CO-Ar mixtures, the mean squared torque increases linearly with the density until densities close to those of the liquid. Therefore the intermolecular torques between CO-CO and CO-Ar must be of very short range. In both the liquid and the high temperature solid the root mean squared torque is about 4 to 5kT per radian. Thus the rotational motion of CO is highly hindered in the liquid and solid. Sufficient data is available so that some checks on the consistency of this interpretation are possible.