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

The valence internally contracted multireference configuration-interaction (icMRCI) method is used to compute potential energy curves (PECs) of the X ¹ Σ ⁺ , A ¹ Π C ¹ Σ ⁻ , D ¹ Δ 2 ¹ Π a ³ Σ ⁺ , b ³ Π d ³ Δ e ³ Σ ⁻ , 2 ³ Δ 2 ³ Σ ⁻ , 1 ⁵ Σ ⁺ and 1 ⁵ Π 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 10 ³ s ⁻¹ for Einstein coefficients. Comparing with experimental measurements, our calculations can well reproduce the band origins and Franck-Condon factors of the A ¹ Π-X ¹ Σ ⁺ system. Similar accuracy is assumed for the other band systems. Many emissions for the A ¹ Π-X ¹ Σ ⁺ , 2 ¹ Π-A ¹ Π 2 ¹ Π-X ¹ Σ ⁺ , 2 ¹ Π-C ¹ Σ ⁻ , 2 ¹ Π-D ¹ Δ b ³ Π-a ³ Σ ⁺ , e ³ Σ ⁻ -b ³ Π 2 ³ Δ-1 ³ Δ 2 ³ Σ ⁻ -1 ³ Σ ⁻ , 2 ³ Σ ⁻ -b ³ Π and 1 ⁵ Π-1 ⁵ Σ ⁺ systems are found to be strong according to our calculated Einstein coefficients, whereas the emissions are weak for the 2 ³ Δ-b ³ Π system. Radiative lifetimes for the first 15 vibrational levels are evaluated to be about tens of nanoseconds for the 2 ¹ Π state, about several hundred nanoseconds for the A ¹ Π state, about several to tens of microseconds for the b ³ Π 2 ³ Δ 2 ³ Σ ⁻ and 1 ⁵ Π states and about several to several hundred microseconds for the e ³ Σ ⁻ state. The results can be used as guidelines for line identification and diagnostics of astrophysical plasma.