Theoretical Study on Low-lying Excited States of the B3 molecule

Abstract The electronic states of the smallest boron cluster B 3 with excitation energies up to 5eV are systematically investigated. Geometries and spectroscopic constants for the low-lying electronic states were calculated using the multireference configuration interaction method with Davidson correction (MRCI+Q). The nondegenerate 1 2 B 2 and 2 2 A 1 states are arising from the degenerate 2 E' state in D 3h symmetry, this is also the case for 2 2 B 2 and 3 2 A 1 . Furthermore, vertical excitation energies, oscillator strengths, main configurations and transitions of the excited state of B 3 were determined. Notably, the theoretically predicted wavelengths for the X 2 A 1 →2 2 A 1 and X 2 A 1 →2 2 B 2 electronic transitions (728 and 457 nm, respectively) exhibit excellent agreements with experimental absorption bands observed at 736 and 458 nm. These theoretical findings provide critical insights into the electronic structure and geometric configuration of the B 3 cluster.