ExoMol molecular line lists – XLIII. Rovibronic transitions corresponding to the close-lying X 2Π and A 2Σ+ states of NaO

The sodium monoxide radical (NaO) is observed in night-glow in the Earth’s mesosphere and likely has astronomical importance. This study concerns the optical transitions within the ground X 2Π state and to the very low-lying (Te ≈ 2000 cm−1) excited A 2Σ+ state. A line list consisting of rovibronic term values, allowed electric dipole transitions, Einstein coefficients, and partition functions for varying temperature are produced using a variational solution of the coupled-channel Schrödinger equations using the program duo. multi-reference configuration interaction (MRCI) ab initio calculations characterizing the potential energy curves of the two states, spin-orbit and L-uncoupling non-adiabatic matrix elements, as well as permanent and transition dipole moments were integral in the formation of the final deperturbation model. Ab initio potential energy curves are represented in the analytical Extended Morse Oscillator form and refined, along with the spin-orbit and L-uncoupling functions, by least-squares fitting to the available spectroscopic data. The input experimental data consisted of pure rotational transitions within the fine-structure components of the X 2Π state for v″ ∈ [0, 3] vibrational levels as well as the rovibronic A 2Σ+(v′ = 0) ← X 2Π(v″ = 0) transitions, both with limited coverage over rotational excitation. The lack of data detailing the vibrational structure of the X and A states points to the need for further experimental study of higher excited levels, which would provide a more robust spectroscopic model. The NaO NaOUCMe line list is available via www.exomol.com and the CDS data base

A coupled-channel deperturbation treatment of the X 2Σ + ∼ A 2Π ∼ B 2Σ + complex of the CN radical towards spectroscopic accuracy

A global deperturbation analysis of the experimental rovibronic term values of the X2Σ+, A2Π and B2Σ+ states of the 12C14N isotopomer has been performed. The inverse spectroscopic problem was directly solved in the framework of the reduced 4×4 coupled-channel (RCC) deperturbation model based on potential energy curves (PECs) as well as the spin-orbit and L-uncoupling electronic matrix elements between the X2Σ+, A2Π, and B2Σ+ states. Regular perturbations of the X∼A∼B complex by the remote doublet states manifold were taken into account by introducing of the fine-structure parameters as explicit functions of interatomic distance. The optimized PECs and non-adiabatic coupling functions describe the vast majority (5600–6570) of the empirical term values, attributed to locally and regularly perturbed levels of the complex, with a root-mean-squared deviation of 0.015-0.05 cm−1, depending on a particular set of the experimental term values included in the fitting procedure. The resulting mass-invariant RCC deperturbation parameters can straightforwardly extend a line-list of all CN isotopomers into a wide region of vibrational and rotational quantum numbers