MRCI study of the spectroscopic parameters and transition properties of the 36 low-lying electronic states of the B molecule.

This paper studied the spectroscopic and transition properties of 36 low-lying states, which came from the first two dissociation limits of B molecule. The potential energy curves were calculated with the complete active space self-consistent field (CASSCF) method, which was followed by the internally contracted multireference configuration interaction (icMRCI) plus Davidson modification (icMRCI+Q) approach. Of these 36 states, the 2Σ, 1Σ, 2Π, and 1Δ states were repulsive; the BΔ, EΣ, fΣ, gΠ, 2Π, 3Σ, 3Π, 1Π, and 3Σ states had double wells; the BΔ, EΣ, GΣ, fΣ, gΠ, 3Σ, 2Π, 3Π, 1Π, 2Π, 2Σ, and 3Σ states had one barrier; the 2Σ state and the second wells of BΔ, EΣ, 1Π, fΣ, gΠ, and 2Π states were weakly bound; and the 2Σ state had no vibrational levels. The avoided crossings existed between the BΔ and 2Δ states, the EΣ and GΣ states, the GΣ and 3Σ states, the 3Σ and 4Σ states, the 2Π and 3Π states, the gΠ and 2Π states, the 2Σ and 3Σ states, the 1Π and 2Π states, the 2Π and 3Π states, the 2Σ and 3Σ states, as well as the FΠ and 3Π states. Core-valence correlation and scalar relativistic corrections were taken into account. The extrapolation to the complete basis set limit was done. The spectroscopic parameters and vibrational properties were obtained. The transition dipole moments were calculated. Franck-Condon factors of some transitions were evaluated. The spin-orbit coupling (SOC) effect on the spectroscopic parameters and vibrational properties is tiny and sometimes even can be negligible. The results determined in this paper can provide some powerful guidelines to observe these states, in particular the states which have not been studied in the experiment.