Theoretical study on the low-lying excited states of the phosphorus monoiodide (PI) including the spin–orbit coupling. (January 2016) - Zhang, Xiaomei
Abstract: The potential energy curves (PECs) of the 22 Λ–S states of the phosphorus monoiodide (PI) molecule have been calculated at the level of MRCI+Q method with correlation-consistent quadruple-ζ quality basis set. The spectroscopic constants of the bound states are determined, which well reproduce the available measurements. The metastable a 1 Δ state has been reported for the first time, which lies between the X 3 Σ − and b 1 Σ + states and have much deeper well than the ground state. The R -dependent spin–orbit (SO) matrix elements are calculated with the full-electron Breit–Pauli operator. Based on the SO matrix elements, the perturbations that the 2 3 Π state may suffer from are analyzed in detail. The SOC effect makes the original Λ–S states split into 51 Ω states. In the zero-field splitting of the ground state X 3 Σ −, the spin–spin coupling contribution (2.23 cm −1 ) is found to be much smaller compared to the spin–orbit coupling contribution (50 cm −1 ). The avoided crossings between the Ω states lead to much shallower potential wells and the change of dissociation relationships of the states. The Ω-state wavefunctions are analyzed depending on their Λ–S compositions, showing the strong interactions among several quasidegenerate Λ–S states of the same total SO symmetry. The transition properties including electric dipole ( E 1), magnetic dipole ( M 1), and electric quadrupole ( E 2) transition moments ( TM s), the Franck–Condon factors, the transition probabilities and the radiative lifetimes are computed for the transitions between Ω components of a 1 Δ and b 1 Σ + states and ground state. The transition probabilities induced by the E 1, E 2, and M 1 transitions are evaluated. The E 2 makes little effect on transition probabilities. In contrast, the E 1 transition makes the main contribution to the transition probability and the M 1 transition also brings the influence that cannot be neglected. Finally, the radiative lifetimes are determined with the transition moments including E 1 and M 1. The lifetime of transition (2)0 + –X1 0 + is evaluated at the level of millisecond, much smaller than that of the transition (2)0 + –X2 1. Highlights: The PECs of the 22 Λ–S states have been calculated. The metastable state a 1 Δ has been studied for the first time. The PECs of the 51 Ω states arising from 22 Λ–S states have been calculated. The perturbations between the states have been studied with SO matrix elements. The coupling among the Λ-S states have been analyzed with Ω-state wavefunctions.