Ab initio study of the first excited state and of the transition of CNO

The potential energy surface of the A 2 Σ + electronic state of CNO is calculated using the cc-pVQZ/MRCI+Q method. The rovibrational levels are determined variationally up to 18 000 cm−1 above the electronic ground state zero energy point and are used with the transition dipole moment surfaces, obtained with the cc-pVQZ/CASSCF method, in order to model the rovibrational absorption A 2 Σ + ← X 2 Π spectrum at 5 K which is compared with the measurement of Bondybey et al. [V.E. Bondybey, J.H. English, C.W. Mathews, R.J. Contolini, Chem. Phys. Lett. 82 (1981) 208].