Extensive spin–orbit multi-reference computations on the excited states of the phosphorus monochloride molecule.

Total 34 Λ-S states of the PCl molecule have been studied by using the multi-reference configuration interaction plus the Davidson correction (MRCI+Q) method with the correlation consistent quadruple-zeta quality basis set. These states are correlated to three dissociation limits P( 4 S u )+Cl( 2 P u ), P( 2 D u )+Cl( 2 P u ), and P( 2 P u )+Cl( 2 P u ), respectively. The potential energy curves (PECs) of the Λ-S states have been calculated, from which the spectroscopic constants of the bound states are determined. The calculated spectroscopic results well reproduce the available measurements. The spin–orbit matrix elements between the Λ-S states have been calculated, which indicate that the perturbations exist in the interacting system 1 1 Π−2 3 Π and 1 1 Π−2 3 Σ − . And the excited a 1 Δ, b 1 Σ + , 2 1 Σ + states could be predissociated induced by the spin–orbit coupling (SOC) effect. The SOC calculation on the PCl molecule has been performed with the state interaction method. This is the first time that the SOC effect of the PCl has been studied theoretically. The SOC effect leads to the 34 Λ-S states split into the 74 Ω states. The ground state X 3 Σ − splits into the X 3 Σ 0 − + (X 1 0 + ) and X 3 Σ 1 − (X 2 1) states. For the zero-field splitting of the X 3 Σ − state, the spin–orbit contribution of 6 cm −1 is much larger than spin-spin contribution of 0.32 cm −1 . Under the influence of the SOC effect, the spectroscopic results of the a 1 Δ and b 1 Σ + states have very small changes, but the dissociation energies strongly decrease. The transition properties of PCl are also predicted, including the E 1, M 1, and E 2 transition moments, the Franck–Condon factors, the transition probabilities, and the radiative lifetimes. For the transitions from a 1 Δ-X 3 Σ − and b 1 Σ + −X 3 Σ − , the transition probabilities are in order of A E 1 > A M 1 ≫ A E 2 . The lifetimes for the b 1 Σ + ( v׳ =0) state are 4.87ms ( E 1) and 4.57 ms ( E 1+ M 1), in good agreement with the available experimental result of 4.9±0.8 ms. [ABSTRACT FROM AUTHOR]