Intensity,transition moment,and bandshapes for the second overtone of compressed CO

Infrared spectra of the CO second overtone absorption band have been studied for pressures up to 156 bar. The absolute intensity, obtained from direct measurements of the total band, is found to be (1.27 ± 0.04) × 10^-2cm^-2Am^-1 at 298 K. Using the vibrational moments for the ground state and the transitions 0–1 to 0–4, we have evaluated the coefficients M₀ to M₄ of the quartic dipole moment function for CO and the coefficients of the vibration-rotation interaction functions. The normalized 0–3 band contours of compressed CO were first generated by summing the pressure-broadened rotational lines with Lorentz profiles. A discrepancy appears between calculated and observed bandshapes and increases with density. An empirical model, which involves the sum of CO self-broadened lines with profile described as the product of a Lorentz function by a fitted exponential function, gives reasonable agreement with the experiments. The interference effects resulting from overlapping lines have been estimated within the impact approximation.