MRCI study on spectroscopic and molecular properties of four low-lying electronic states of the BO radical

The potential energy curves (PECs) of four low-lying electronic states of the BO radical, including two 2Σ+ and two 2Π states, have been studied using the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in combination with the cc-pV5Z basis set for internuclear separations from 0.05 to 2.0 nm. The effect on the PECs by the relativistic correction has been taken into account. With these PECs, the spectroscopic parameters (Te, D0, De, Re, ωe, ωexe, αe and Be) of two main isotopologues (11B16O and 10B16O) have been determined. These parameters have been compared in detail with those of previous investigations reported in the literature, and excellent agreement has been found between the available data and the present results. By solving the radial Schrödinger equation of nuclear motion, 60 vibrational states for the 11B16O(X2Σ+), 60 for the 10B16O(X2Σ+), 66 for the 11B16O(A2Π) and 64 for the 10B16O(A2Π) are predicted for the non-rotating molecule. For each vibrational state of the 11B16O(X2Σ+), 10B16O(X2Σ+), 11B16O(A2Π) and 10B16O(A2Π), the vibrational level G(υ), inertial rotation constant Bυ and centrifugal distortion constant Dυ have been determined. Comparison with the available data shows that the present molecular constants are reliable and accurate. The ro-vibrational levels have been calculated for the X2Σ+ and A2Π states of two main species for future laboratory research.