Theoretical spectroscopic calculations on the 25 Λ–S and 66 Ω states of [formula omitted] cation in the gas phase including the spin–orbit coupling effect

Abstract

The potential energy curves (PECs) of 66 Ω states generated from the 25 Λ–S states are studied in detail with an ab initio quantum chemical method. All these 25 Λ–S states correlate to the first three dissociation limits of the N2+ cation, of which only the 16Σu+ is the repulsive and only the A2Πu, D2Πg, f4Πu and 12Φg are the inverted ones with the spin–orbit coupling included. The PECs are calculated for internuclear separations from about 0.10 to 1.10nm by the CASSCF method, which is followed by the internally contracted MRCI approach with Davidson correction. The spin–orbit coupling is accounted for by the state interaction approach with the Breit–Pauli Hamiltonian using an all-electron aug-cc-pCV5Z basis set. The convergent behavior is discussed with respect to the basis set and level of theory. Core–valence correlation corrections are included by using an aug-cc-pCV5Z basis set. Scalar relativistic corrections are calculated by the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. All these PECs are extrapolated to the complete basis set limit. With these PECs, the spectroscopic parameters of 24 Λ–S and 63 Ω bound states are evaluated by fitting the first ten vibrational levels whenever available, which are determined by solving the rovibrational Schrödinger equation with the Numerov׳s method. The energy splitting in the A2Π Λ–S state is determined to be 72.67cm−1, which agrees favorably with the measurements of 75.07cm−1. Moreover, other spectroscopic parameters of Λ–S and Ω states involved here are also in fair agreement with available measurements. It demonstrates that the spectroscopic parameters reported in this paper can be expected to be reliably predicted ones.