Ab initio MO study of the A, D and third 2Π states of CO+

Ab initio MO calculations were performed for three lowest doublet Pi states of CO+ using the multireference configuration interaction method. Some spectroscopic constants were evaluated also for other low-lying states. For the X(2)Sigma(+) A(2)Pi, and B(2)Sigma(+) states, the calculated spectroscopic constants are in very good agreement with experimental data within the limit of experimental accuracy. In the photoelectron spectra, a series of the vibrational progression assigned to the D 2(2)Pi stare persists up to nu = 9, whereas the calculated adiabatic potential energy holds only three vibrational levels below a barrier at R = 1.44 Angstrom, which results from an avoided crossing with the upper state, third (2)Pi. The observed progression was analyzed in terms of the resonant states obtained from the coupling of two strongly interacting diabetic states, second and third (2)Pi. (C) 2000 Elsevier Science B.V. All rights reserved.