Theoretical study of the ro-vibrational spectrum of CaO molecule in its two X1Σ+ and A1Σ+ states

•The best basis set is the aug-cc-pV5Z for O and the cc-pCV5Z for Ca and the active space is chosen for 4220.•The comprehensive line intensities are computed for X1Σ+ 1-0, 2-1, 3-2, 4-3, 2-0, 3-1, and 4-2 bands.•The transition dipole moment A1Σ+–X1Σ+ and line intensities for A1Σ+(v = 0)–X1Σ+(v = 0) band are firstly calculated.

Highly correlated ab initio calculations were performed for accurate determination of the lowest two 1Σ+ states of CaO molecule. Highly accurate multi-reference configuration interaction (MRCI) approach and active space (4220) were used to investigate the potential energy curves (PECs) and dipole moment curves (DMCs) of X1Σ+ and A1Σ+ states. The PECs of the two states agree well with Rydberg–Klein–Rees (RKR) potential. Computations were performed using aug-cc-pV5Z basis set for O and cc-pCVnZ for Ca. Partition function was calculated using two different methods to obtain the spectral absolute intensity from 100 K to 1000 K. Moreover, the ro-vibrational transition dipole moments and Einstein A coefficient were calculated to predict the line lists of ro-vibrational spectral intensities. The line lists of the X1Σ+ included 1-0, 2-1, 3-2, 4-3, 2-0, 3-1, and 4-2 bands. This study is the first to calculate the transition dipole moment of A1Σ+–X1Σ+ and line intensities of 1-0 band.

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