The A2Πi∼X2Σ+ interaction in CO+: Deperturbation analyses of B-A and A-X bands of 12C16O+, 13C16O+ and 14C16O+

The 1-0, 6-0 and 6-1 bands of the A2Πi→X2Σ+ system of 13C16O+ and the 2-0 and 2-1 bands of the A2Πi→X2Σ+ system of 14C16O+ have been recorded at high resolution for the first time. The 0-2 and 5-0 bands of the A → X system of 12C16O+ have also been recorded at higher resolution than in previous work. The spectra were excited in an air-cooled hollow cathode discharge and photographed using a 2-m plane grating spectrograph. The spectral resolution and the Doppler-broadened line widths are both ∼0.12 cm−1, and the experimental measurement precision of resolved lines is ∼0.02 cm−1. The measured line positions, sometimes in combination with literature data on the B2Σ+→A2Πi transition, have been employed in deperturbation analyses of level crossings in the near-degenerate A(0)∼X(10) and A(5)∼X(14) interactions in 12C16O+, the A(1)∼X(11) and A(6)∼X(15) interactions in 13C16O+, and the A(2)∼X(12) interaction in 14C16O+. No radial dependence of the electronic perturbation matrix elements HSO(r) and HRE(r) could be detected over the narrow range of r-centroids (1.477-1.501 Å), and the mean values of these parameters are HSO = −49.06(15) cm−1 and HRE = 0.211(2). Using iteratively improved RKR potentials and FC-overlap integrals, the mean HSO and HRE were employed in least-squares analyses of A → X literature data involving A(υ) levels of the three isotopologues that are affected by interactions with one or two distant X(υ∗) levels. The fitted parameters of the A2Πi state (Bυ, Aυ, ADυ, pυ, qυ) exhibit υ-dependences that are much smoother than those employing perturbed parameters determined in previous investigations. In addition, a significant electronic isotope effect has been characterized. The separations Te(A)-Te(X) of the minima of the A and X states of 13C16O+ and 14C16O+ are less than that of 12C16O+ by 0.39 and 0.73 cm−1, respectively. Although Born-Oppenheimer breakdown of this magnitude is surprising, it is similar to that found for the B2Σ+ state of CO+.