Improved Hot Line Lists for Minor CN Isotopologues in the X 2 Σ + , A 2 Π, and B 2 Σ + Systems Using Diagonal Born–Oppenheimer Corrections

Abstract We present improved hot line lists for optical transitions between the mutually perturbed B 2 Σ + , A 2 Π, and X 2 Σ + states of the minor CN isotopologues 13 C 14 N, 12 C 15 N, and 13 C 15 N. Accurate line positions and intensities for these isotopologues are required for high-resolution analyses of stellar CN red-system spectra and cometary CN violet-band fluorescence, where minor-isotopologue features are used to infer carbon and nitrogen isotopic ratios. The rovibronic energies and transition probabilities were recalculated by explicitly incorporating mass-dependent diagonal Born–Oppenheimer corrections (DBOCs) into the semiempirical potential energy curves recently derived for the B , A , and X states for the main 12 C 14 N isotopologue. For the X and A states, the radial DBOC functions were initially estimated during electronic structure calculations accomplished at the CCSDT/cc-pVDZ level of theory. The inclusion of the ab initio DBOCs significantly improves the accuracy of the A − X and B − X positions by reducing the root-mean-square error (RMSE) in the description of the experimental A − X and B − X lines of the 13 C 14 N [ 12 C 15 N] isotopologues from 0.24 [0.15] and 0.16 [0.05] cm −1 to 0.04 [0.01] and 0.08 [0.05] cm −1 , respectively. A subsequent simultaneous adjustment of the DBOC functions for all three B , A , and X states to the experimental 13 C 14 N lines further decreased the RMSE of the predicted wavenumbers for the minor 13 C 14 N and 12 C 15 N isotopologues to the spectroscopic level of accuracy. The new KTPSYT-iso line lists are made available via www.exomol.com .