Low-lying electronic states in bismuth trimer Bi₃ as revealed by laser-induced NIR emission spectroscopy in solid Ne

Laser-induced near-infrared (NIR) emission spectra of neutral bismuth timer, Bi₃, embedded in solid neon matrixes at 3 K were recorded in a range 870-1670 nm. Using photoexcitation with low energy photons at 1064 nm, two emission band systems were newly identified by their origin bands at T₀ = 6600 and 8470 cm⁻¹. Accordingly, spectral assignment for three NIR emission band systems reported recently was partly revised for the one with its origin band at T₀ = 7755 cm⁻¹ and reconfirmed for the others at T₀ = 9625 and 11,395 cm⁻¹. Energy splitting by spin-orbit coupling between the pair of electronic energy levels in the ground state of bismuth trimer, Bi₃, both having a totally symmetric vibrational mode of frequency at ω(e)" = 150 cm⁻¹, was determined to be 1870 ± 1.5 cm⁻¹. Transitions from the pair of electronically excited states, locating at T₀ = 8470 and 9625 cm⁻¹ above the ground state and separated by spin–orbit coupling of 1155 cm⁻¹, have relatively long decay constants of τ ∼0.2 and ∼0.1 ms, respectively.