MRCI study of the spectroscopic parameters and transition properties of the 36 low-lying electronic states of the B2 molecule

The PECs of 36 states of B2 molecule were calculated using the CASSCF method followed by the icMRCI + Q approach. The spectroscopic and transition properties were evaluated. The 25Σu−, 15Σu+, 25Πu, and 15Δu states were repulsive. The B3Δu, E3Σu+, f1Σu−, g1Πg, 23Πu, 33Σg−, 33Πu, 15Πg, and 33Σu+ states had double wells. The avoided crossings existed between the B3Δu and 23Δu states, the E3Σu+ and G3Σu+ states, the G3Σu+ and 33Σu+ states, the 33Σu+ and 43Σu+ states, the 23Πu and 33Πu states, the g1Πg and 21Πg states, the 15Πg and 25Πg states, the 23Σg− and 33Σg− states, the 25Πg and 35Πg states, the 25Σg− and 35Σg− states, and the F3Πg and 33Πg states. The second wells of B3Δu, E3Σu+, 15Πg, f1Σu−, g1Πg, and 23Πu states were very weakly bound and very difficult to observe. The 25Σg− state was very weakly bound and had no vibrational levels. All the bound states except for the second wells noted above can be detected by observing the transitions proposed here. On the whole, the SOC effect on the spectroscopic and transition properties is very tiny. These spectroscopic and transition properties can provide some powerful guidelines to detect these states, in particular for the states which have not been observed in the experiment.146