Measurement and calculation of CO (7-0) overtone line intensities

Intensities of 14 lines in the sixth overtone (7-0) band of carbon monoxide (¹²C¹⁶O) are measured in the visible range between 14 300 and 14 500 cm⁻¹ using a frequency-stabilized cavity ring-down spectrometer. This is the first observation of such a high and weak overtone spectrum of the CO molecule. A theoretical model is constructed and tested based on the use of a high accuracy ab initio dipole moment curve and a semi-empirical potential energy curve. Accurate studies of high overtone transitions provide a challenge to both experiment and theory as the lines are very weak: below 2 × 10⁻²⁹ cm molecule⁻¹ at 296 K. Agreement between theory and experiment within the experimental uncertainty of a few percent is obtained. However, this agreement is only achieved after issues with the stability of the Davidson correction to the multi-reference configuration interaction calculations are addressed.