Potential energy curves and transition properties for the ground and excited states of BH+ cation

BH+ cation is one of the candidates for laser cooling. The potential energy curves (PECs) for nine electronic states (X2+, A2, B2+, a4, b4+, 32+, 22, 32, 42+) relating to the B+(1Sg)+H(2Sg), B+(3Pu)+H(2Sg), B(2Pu)+H+(1Sg), and B+(1Pu)+H(2Sg) dissociation channels of BH+ cation are obtained using highly accurate multi-reference configuration interaction (MRCI) plus Davidson correction. All-electron basis sets AV5Z-DK for H and ACV5Z-DK for B are used in PEC calculations for the -i-S states of BH+ cation, respectively. In complete active space self-consistent field (CASSCF) calculation, H(1s2s2p3s3p) and B(2s2p) are chosen as active orbitals, B(1s) is the closed shell; in the MRCI calculation, the core-valence (CV) correction is considered, i.e., B(1s) shell is used for CV correlation. Spin-orbit coupling effects are considered with Breit-Pauli operators. Spectroscopic constants are fitted using the Murrell-Sorbie function. Spectroscopic constants for the X2+, A2, and B2+ states are in excellent agreement with the available experimental data; spectroscopic constants for the b4+, 32+, 32, and 42+ states are reported. Two potential wells for the 32 and 42+ states are found. The maximum fitting error of all electronic states is only 3.407 cm-1. In addition, PECs for the A2 and B2+ states are crossed at about 2.7 . Then, the transition dipole moments (TDMs) for the A2 X2+, B2+X2+, 32+X2+, B2+ A2, 32 X2+ and b4+ a4 transitions are also obtained. The strength for the B2+ A2 transition is very weak. Based on the accurate PECs and TDMs, the Franck-Condon factors and spontaneous radiative lifetimes are calculated. A strongly diagonal Franck-Condon factor (f00) for the A2X2+ transition is obtained, which equals 0.9414. Spontaneous radiative lifetime for the A2 and B2+ states is also predicted. i.e., (A2)=239.2 ns and (B2+)=431.2 ns. When SOC effect is considered, the A21/2 and B21/2+ states avoid crossing in the Franck-Condon region (R is about 2.7 ). Calculated f00 for the A21/2 X21/2+ transition is 0.9430; spontaneous radiative lifetime for the A21/2 is 239.0 ns. Our calculated results indicate that the influence for laser cooling BH+ cation via the crossing between B2+ and A2 states can be ignored.