High-resolution Fourier transform spectroscopy of the CaO A1Σ+ − X1Σ+ transition: New insights into perturbations by the a3Π0+ and A1Πstates

The emission spectrum of the A1Σ+ − X1Σ+ transition of CaO has been recorded at a resolution of 0.03 cm−1 using a Fourier transform spectrometer in the 10 000-15 000 cm−1 spectral range. New information has been collected for the low-J term values of several vibrational levels of the A1Σ+ state and also for the perturbing states. For example, about 40 term values of a3Π0+(v=6) level [which perturbs the A1Σ+ (v = 0) level] have been identified for the first time. A least squares procedure has been used to determine the vibrational and rotational constants of these states. In each case an empirical 2 × 2 matrix has been used with an off-diagonal term linking the two electronic states to account for the interaction. Our study is limited to perturbations for which extensive experimental information is available for both interacting states. The derived constants, especially the off-diagonal coupling constants, are in agreement with those published by R.W. Field [J. Chem. Phys. 60 (1974) 2400-2413].