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

•Lifetimes are 10–4 s for the C4Δ state, and 10–7 s for the B4Σ– and E4Π states.•B4Σ– – X4Σ–, E4Π – X4Σ–, E4Π – A4Π, and E4Π – B4Σ– transitions are strong.•Lifetimes are 10–2 – 10–4 s for the D4Σ+ state and 10–3–10–4 s for the A4Π state.•Lifetimes are 10–5 s for the b2Σ– and d2Σ+ states, and 10–4–10–5 s for the c2Δ state.•E4Π – C4Δ and E4Π – D4Σ+ transitions are weak. Several experimental groups have measured the rovibrational transitions of B4Σ– – X4Σ–, 24Π – X4Σ–, B4Σ– – A4Π, and d2Σ+ – a2Π 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 X4Σ–, A4Π, B4Σ–, 14Δ, 14Σ+, and 24Π states, between the a2Π, b2Σ–, c2Δ, and d2Σ+ states, and from the a2Π3/2 and a2Π1/2 states to the X4Σ–3/2 and X4Σ–1/2 states. The radiative lifetimes are on the order of 10–2 – 10–4 s for the 14Σ+ state, 10–3 – 10–4 s for the A4Π state, 10–4 s for the 14Δ state, 10–4 – 10–5 s for the c2Δ state, 10–5 s for the b2Σ– and d2Σ+ states, and 10–7 s for the B4Σ– and 24Π states. The B4Σ– – X4Σ–, 24Π – X4Σ–, 24Π – A4Π, and 24Π – B4Σ– transitions are strong. The transitions from the a2Π1/2 and a2Π3/2 states to the X4Σ–1/2 and X4Σ–3/2 states are weak. The emissions originating from the a2Π1/2 and a2Π3/2 states at higher vibrational levels are easier to measure than those at lower levels. The radiative lifetimes are approximately 100 – 103 and 100 – 102 s for the a2Π1/2 and a2Π3/2 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 A4Π, B4Σ–, 24Π, b2Σ–, and d2Σ+ states. The transition properties reported in this work can provide useful guidelines for future experimental and theoretical studies. [Display omitted] The TDMs are calculated for the transitions between the six lowest–lying quartet states, between the four lowest–lying doublet states, and from the a2Π1/2 and a2Π3/2 states to the X4Σ–1/2 and X4Σ–3/2 states. The radiative lifetimes are approximately 10–2 – 10–4 s for the D4Σ+ state, 10–3 – 10–4 s for the A4Π state, 10–4 s for the C4Δ state, 10–4 – 10–5 s for the c2Δ state, 10–5 s for the b2Σ– and d2Σ+ states, and 10–7 s for the B4Σ– and E4Π states. The radiative lifetimes are on the order of several to several–thousand seconds for the a2Π1/2 stat