Radiative lifetimes of several low-lying doublet and quartet electronic states of diatomic boron carbide

Several experimental groups have measured the rovibrational transitions of B-4 Sigma(-) - X-4 Sigma(-), 2(4)Pi - X-4 Sigma(-), B-4 Sigma(-) - A(4)Pi, and d(2)Sigma(+) - a(2)Pi systems of diatomic boron carbide. However, no transition properties between any electronic states of this molecule have been calculated. This work studied the transition dipole moments between the X-4 Sigma(-), A(4)Pi, B-4 Sigma(-), 1(4)Delta, 1(4)Sigma(+), and 2(4)Pi states, between the a(2)Pi, b(2)Sigma(-), c(2)Delta, and d(2)Sigma(+) states, and from the a(2)Pi(3/2) and a(2)Pi(1/2) states to the X-4 Sigma(-)(3/2) and X-4 Sigma(-)(1/)(2) states. The radiative lifetimes are on the order of 10(-2) - 10(-4) s for the 1(4) Sigma(+) state, 10(-3) - 10(-4) s for the A(4)Pi state, 10(-4) s for the 1(4)Delta state, 10(-4) - 10(-5) s for the c(2)Delta state, 10(-5) s for the b(2)Sigma(-) and d(2)Sigma(+) states, and 10(-7) s for the B-4 Sigma(-) and 2(4)Pi states. The B-4 Sigma(-) - X-4 Sigma(-) , 2(4)Pi - X-4 Sigma(-), 2(4)Pi - A(4)Pi, and 2(4)Pi - B-4 Sigma(-) transitions are strong. The transitions from the a(2)Pi(1/2) and a(2)Pi(3/2) states to the X-4 Sigma(-)(1/)(2) and X-4 Sigma(-)(3/2) states are weak. The emissions originating from the a(2)Pi(1/2) and a(2)Pi(3/2) states at higher vibrational levels are easier to measure than those at lower levels. The radiative lifetimes are approximately 10(0) - 10(3) and 10(0) - 10(2) s for the a(2)Pi(1/2) and a(2)Pi(3/2) states, respectively. The band origins, Franck-Condon factors, and Einstein A coefficients of all dipole-allowed transitions were calculated. The distribution of radiative lifetime varying with rotational angular quantum number was investigated for the A(4)Pi, B-4 Sigma(-), 2(4)Pi, b(2)Sigma(-), and d(2)Sigma(+) states. The transition properties reported in this work can provide useful guidelines for future experimental and theoretical studies. (C) 2020 Elsevier Ltd. All rights reserved.