Energy levels, transition dipole moment, transition probabilities and radiative lifetimes for low-lying electronic states of PN

Abstract

The valence internally contracted multireference configuration-interaction (icMRCI) method is used to compute potential energy curves (PECs) of the X1Σ+, A1Π, C1Σ−, D1Δ, 21Π, a3Σ+, b3Π, d3Δ, e3Σ−, 23Δ, 23Σ−, 15Σ+ and 15Π states for PN, together with the Davidson, core-valence (CV) and scalar relativistic corrections, as well as the basis-set extrapolation. Transition dipole moments (TDMs) of fifteen dipole-allowed transitions between the thirteen states are calculated by the icMRCI approach with the aug-cc-pV6Z basis set. The vibrational band origins, Einstein coefficients and Franck-Condon factors of all spontaneous emissions for the fifteen band systems are determined, seeking to theoretically predict the strong emissions at least of the order of 103 s−1 for Einstein coefficients. Comparing with experimental measurements, our calculations can well reproduce the band origins and Franck-Condon factors of the A1Π-X1Σ+ system. Similar accuracy is assumed for the other band systems. Many emissions for the A1Π-X1Σ+, 21Π-A1Π, 21Π-X1Σ+, 21Π-C1Σ−, 21Π-D1Δ, b3Π-a3Σ+, e3Σ−-b3Π, 23Δ-13Δ, 23Σ−-13Σ−, 23Σ−-b3Π and 15Π-15Σ+ systems are found to be strong according to our calculated Einstein coefficients, whereas the emissions are weak for the 23Δ-b3Π system. Radiative lifetimes for the first 15 vibrational levels are evaluated to be about tens of nanoseconds for the 21Π state, about several hundred nanoseconds for the A1Π state, about several to tens of microseconds for the b3Π, 23Δ, 23Σ− and 15Π states and about several to several hundred microseconds for the e3Σ− state. The results can be used as guidelines for line identification and diagnostics of astrophysical plasma.