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

This study addresses the transition properties of the X-3 Pi, A(3)Sigma+, B-3 Sigma(-), C-3 Pi, D-3 Pi, E-3 Sigma(+), a(1)Sigma(+), b(1)Pi, c(1)Delta, and d(1)Sigma(+) 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 E-3 Sigma(+) state, 10(-7)-10(-8) s for the C-3 Pi state, 10(-7) s for the D-3 Pi and d(1)Sigma(+) states, 10(-6) s for the c(1)Delta state, 10(-5)-10(-6) s for the B-3 Sigma(-) state, and 10(-5) s for the A(3)Sigma(+) and b(1)Pi states. The C-3 Pi - X-3 Pi and E-3 Sigma(-)- X-3 Pi transitions are strong, followed by the D-3 Pi - X-3 Pi, D-3 Pi - B-3 Sigma(-), E-3 Sigma(-) - A(3)Sigma(+), d(1)Sigma(+) - a(1)Sigma(+), and d(1)Sigma(+) - b(1)Pi transitions. The spin-forbidden transitions from the a(1)Sigma(+) and b(1)Pi states to the X-3 Pi state are calculated and confirmed to be weak. The radiative lifetimes of all the vibrational levels are approximately 10(-1) s for the a(1)Sigma(+)(0+) state. The contribution of the b(1)Pi - X-3 Pi transition to the radiative lifetimes of the b(1)Pi 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 nu of the A(3)Sigma(+), B-3 Sigma(-), C-3 Pi, D-3 Pi, E-3 Sigma+, b(1)Pi, and c(1)Delta states when nu <= 15. The transition properties reported in this study can provide useful guidelines for future investigations, both experimentally and theoretically. (C) 2020 Elsevier Ltd. All rights reserved.