Abstract
The rovibronic structure of A2Σ+, B2Π, and C2Π states of nitric oxide (NO) is studied with the aim of producing comprehensive line lists for its near ultraviolet spectrum. Empirical energy levels for the three electronic states are determined using a combination of the empirical measured active rotation-vibration energy level (MARVEL) procedure and ab initio calculations, and the available experimental data are critically evaluated. Ab initio methods that deal simultaneously with the Rydberg-like A2Σ+ and C2Π and the valence B2Π state are tested. Methods of modeling the sharp avoided crossing between the B2Π and C2Π states are tested. A rovibronic Hamiltonian matrix is constructed using the variational nuclear motion program Duo whose eigenvalues are fitted to the MARVEL. The matrix also includes coupling terms obtained from the refinement of the ab initio potential energy and spin-orbit coupling curves. Calculated and observed energy levels agree well with each other, validating the applicability of our method and providing a useful model for this open shell system.
Highlights
Nitric oxide (NO) is one of the principle oxides of nitrogen
A major issue in generating a UV line list for NO results from the difficulty of modelling the interaction between B 2Π and C 2Π states, which is caused by the particular electronic structure of NO
The rovibronic energy levels of A 2Σ+, B 2Π and C 2Π states were reconstructed by MARVEL analysis of the experimental transitions of the γ, β, δ, and Heath systems and those inside the ground state
Summary
Nitric oxide (NO) is one of the principle oxides of nitrogen. It plays a significant role in the nitrogen cycle of our atmosphere and causes problems of air pollution and acid rain. A major issue in generating a UV line list for NO results from the difficulty of modelling the interaction between B 2Π and C 2Π states, which is caused by the particular electronic structure of NO. To understand this fifteen electrons system one must analyse the electron configuration of these states from the perspective of molecular orbitals. Further analysis was made by Gallusser and Dressler, who set up a vibronic interaction matrix of five 2Π states and fitted the eigenvalues of the matrix to experimental data in the determination of RKR potential curves and off-diagonal electronic energies. The previous works provide us strong inspiration, the task is still challenging due to the interactions between Rydberg and valence states of NO
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