Bandshapes and dipole correlation functions for the first overtone of CO compressed by N 2

Abstract

Infrared spectra of the first overtone absorption band of CO compressed by N 2 at pressures up to nearly 1000 bar have been studied at room temperature. The integrated intensities, as well as the wavenumbers of the maximum absorption for the P- and R-branches and of the minimum absorption between these branches, have been measured as functions of the N 2 density. The dipole moment autocorrelation function has been used to assess the Gordon J-diffusion model and the semi-classical M-model. The normalized band contours are calculated by summing the absorption coefficients for the pressure-broadened rotational lines with a modified Lorentz shape derived from an analysis of individual lines. This model gives reasonable agreement with experiments for densities below 200 Am. The discrepancy between calculated and experimental bandshapes, which increases with density, may be caused by strong overlapping effects and a probable nonlinear variation of the linewidths with density. Consideration of interferences between adjacent rotational lines in the frame of the impact approximation would not be sufficient to provide satisfactory agreement with the experimentally observed band contours.