Radiative properties of the six lowest–lying triplet and four lowest–lying singlet states of boron nitride molecule

Abstract

This study addresses the transition properties of the X3Π, A3Σ+, B3Σ–, C3Π, D3Π, E3Σ+, a1Σ+, b1Π, c1Δ, and d1Σ+ states of the boron nitride molecule. The potential energy curves and transition dipole moments are calculated using the complete active space self–consistent field method, followed by the valence internally contracted multireference configuration interaction approach. The radiative lifetimes are of the order of 10–8 s for the E3Σ+ state, 10–7–10–8 s for the C3Π state, 10–7 s for the D3Π and d1Σ+ states, 10–6 s for the c1Δ state, 10–5–10–6 s for the B3Σ– state, and 10–5 s for the A3Σ+ and b1Π states. The C3Π – X3Π and E3Σ– – X3Π transitions are strong, followed by the D3Π – X3Π, D3Π – B3Σ–, E3Σ– – A3Σ+, d1Σ+ – a1Σ+, and d1Σ+ – b1Π transitions. The spin–forbidden transitions from the a1Σ+ and b1Π states to the X3Π state are calculated and confirmed to be weak. The radiative lifetimes of all the vibrational levels are approximately 10–1 s for the a1Σ+0+ state. The contribution of the b1Π – X3Π transition to the radiative lifetimes of the b1Π state is sufficiently insignificant to be considered negligible. The Franck–Condon factors, Einstein A coefficients, and band origins of all the spontaneous vibronic emissions from all these transitions involved herein are calculated. The distribution of the radiative lifetime varying with rotational angular quantum number J is investigated at J ≤ 70 for a certain vibrational level υ of the A3Σ+, B3Σ–, C3Π, D3Π, E3Σ+, b1Π, and c1Δ states when υ ≤ 15. The transition properties reported in this study can provide useful guidelines for future investigations, both experimentally and theoretically.