Extensive ab initio study of the electronic states of CP radical including spin–orbit coupling

Abstract

The potential energy curves (PECs) of 18 Λ–S states and 13 Ω states generated from six Λ–S states of the CP radical are studied in detail using an ab initio quantum chemical method. All the PEC calculations are performed for internuclear separations from 0.10 to 1.11nm by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson modification. The spin–orbit (SO) coupling effect is accounted for by the Breit-Pauli Hamiltonian. To discuss the effect on the energy splitting by the core-electron correlations, two all-electron basis sets, cc-pCVTZ and cc-pVTZ, are used for the SO coupling calculations. In order to improve the quality of the PECs, core–valence correlation and scalar relativistic corrections are included. Core–valence correlation corrections are taken into account with a cc-pCVTZ basis set. Scalar relativistic correction calculations are carried out using the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. The spectroscopic parameters of 17 Λ–S bound states and 13 Ω states are calculated. When the core-electron correlations are used to calculate the SO coupling splitting by the all-electron cc-pCVTZ basis set and when the core–valence correlation and scalar relativistic corrections are included in the PECs, the SO coupling splitting energy between the A2Π3/2 and A2Π1/2 Ω states is 153.63cm−1, which agree well with the measurements of 157.87cm−1. Moreover, other spectroscopic parameters are also in excellent agreement with the available experimental ones. It demonstrates that the spectroscopic parameters of 14Σ+, 14Δ, 14Π, 22Π, 16Σ+, 14Σ−, 32Π, 12Δ, 12Σ−, 22Δ, 22Σ−, 24Δ, 24Σ− and 26Σ+ Λ–S states and 13 Ω states reported here can be expected to be reliable predicted ones.