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

Abstract

Intensities of 14 lines in the sixth overtone (7–0) band of carbon monoxide (12C 16O) 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.