Extensive calculations on 12 Λ-S and 27 Ω states of PCl+ cation including spin–orbit coupling

Abstract

The potential energy curves (PECs) of 27 Ω states generated from the 12 Λ-S states (X2Π, A2Π, 14Π, 24Π, 12Σ−, 22Σ−, 14Σ−, 24Σ−, 12Σ+, 14Σ+, 12Δ and 14Δ) of PCl+ cation are studied for the first time for internuclear separations from about 0.10 to 1.10nm using an ab initio quantum chemical method. All the 12 Λ-S states correlate to the first dissociation channel of PCl+ cation. Of these Λ-S states, the 24Π is found to be the repulsive one. The 14Σ+, 12Δ and 14Δ are found to be the inverted ones. And the 12Δ is found to possess the double wells. The PECs are calculated by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson correction in combination with the correlation-consistent basis sets, aug-cc-pV(n+d)Z. The effect of core–valence correlation and scalar relativistic corrections on the spectroscopic parameters is briefly discussed. Scalar relativistic corrections are included by the third-order Douglas–Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. Core–valence correlation corrections are included with a cc-pCVTZ basis set. The convergent behavior of present calculations is discussed with respect to the basis set and level of theory. The spin–orbit coupling is accounted for by the state interaction method with the Breit–Pauli Hamiltonian using the all-electron cc-pCVTZ basis set. All the PECs are extrapolated to the complete basis set limit. The spectroscopic parameters are evaluated for the 11 Λ-S bound states and for the 23 Ω bound states, and are compared with available experimental and other theoretical results. Fair agreement has been found between the present spectroscopic parameters and the measurements. The energy splitting in the X2Π Λ-S state is calculated to be 346.11cm−1, close to the estimated measurements of 370cm−1. It demonstrates that the spectroscopic parameters reported here can be expected to be reliably predicted ones.