Radiative lifetimes of several doublet and quartet states of silicon boride

•Lifetimes are 1–10, 0.1–1, and 1 μs for the A4Π, D4Σ–, and E4Π states, respectively.•Lifetimes are 10–100 and 1 – 10 μs for the d2Σ+ and e2Π states, respectively.•Lifetimes are 0.1–103 and 0.1–102 ms for the b2Δ and c2Σ– states, respectively.•Lifetimes are 1–104 and 1–103 ms for the B4Δ and C4Σ+ states, respectively.•A4Π – X4Σ–, D4Σ– – X4Σ–, E4Π – X4Σ–, and E4Π – A4Π transitions are strong. In this study, the potential energy curves were calculated for the X4Σ–, A4Π, B4Δ, C4Σ+, D4Σ–, E4Π, a2Π, b2Δ, c2Σ–, d2Σ+, and e2Π states of silicon boride. The transition dipole moments were computed for all dipole–allowed transitions between these states. The complete active space self-consistent field method was used for calculations, followed by the valence internally contracted multireference configuration interaction approach. The radiative lifetimes were approximately 1 – 10 μs, 0.1 – 1 μs, 1 – 10,000 ms, 1 – 1000 ms, and 1 μs for the A4Π, D4Σ–, B4Δ, C4Σ+, and E4Π states, respectively. Of these transitions between the six lowest–lying quartets, the spontaneous emissions from the A4Π – X4Σ–, D4Σ– – X4Σ–, E4Π – X4Σ–, and E4Π – A4Π systems were strong, whereas those from the B4Δ – A4Π, C4Σ+ – A4Π, and E4Π – B4Δ transitions were weak. The radiative lifetimes were approximately 0.1 – 1000 ms, 0.1 – 100 ms, 10 – 100 μs, and 1 – 10 μs for the b2Δ, c2Σ–, d2Σ+, and e2Π states, respectively. Of the transitions between the a2Π, b2Δ, c2Σ–, d2Σ+, and e2Π states, the spontaneous emissions from the e2Π – b2Δ and e2Π – c2Σ– systems were relatively strong, whereas those from the b2Δ – a2Π transition were relatively weak. The transition frequencies, Einstein A coefficients, and Franck–Condon factors of all spontaneous vibronic bands from these transitions were calculated. The results obtained in this study were compared with experimental and other theoretical values. The radiative–lifetime distribution varying with rotational angular quantum number J was calculated when J ≤ 50.5 for a particular vibrational level of these states. The radiative lifetimes are approximately 1 – 10, 0.1 – 1, 1, 10 – 100, and 1 – 10 μs for the A4Π, D4Σ–, E4Π, d2Σ+, and e2Π states, respectively; and those are of the order of 0.1 – 1000, 0.1 – 100, 1 – 10,000, 1 – 1000 ms for the b2Δ, c2Σ–, B4Δ, and C4Σ+ states, respectively. Of the transitions between the quartet states, the A4Π – X4Σ–, D4Σ– – X4Σ–, E4Π – X4Σ–, and E4Π – A4Π transitions are strong, whereas the B4Δ – A4Π, C4Σ+ – A4Π, and E4Π – B4Δ transi