Accurate vibration-rotation spectra of X1Σ+ and A1Π in BH molecule with explicitly correlated method

High-level ab initio calculations on the ground state X1Σ+ and the excited state A1Π of the BH molecule were carried out by using the explicitly correlated multireference configuration interaction method (MRCI-F12) plus Davidson correction (+Q) and scalar relativistic correction (+SR). The potential energy curves (PECs) of the X1Σ+ and A1Π states were obtained. From the computed PECs, the spectroscopic constants were determined, which are close to the observed values. Further comparisons show that the spectroscopic results determined by the MRCI-F12+Q+SR method have the best accuracy. Therefore, the PECs from the MRCI-F12+Q+SR calculation are used for the determination of the vibrational wavefunctions for the X1Σ+ and A1Π states. And the corresponding vibrational levels ΔGv, vibration-dependent rotational constant Bv and centrifugal distortion constant Dv were calculated. Finally, the transition properties of the A1Π-X1Σ+, including Franck-Condon factors, transition energies and radiative lifetimes of the A1Π state, were obtained and found to be in good agreement with the available experiments. The computed results are helpful to further experimental study of laser cooling BH molecule. AMS subject classifications: 81V45, 81V55, 70F07