Calculations on thirteen Λ-S states of PO radical: Electronic structure, spectroscopy and spin-orbit coupling

This paper presents the potential energy curves (PECs) of X2Π, B2Σ+, B′2Π, C2Σ−, C′2Δ, 32Π, a4Π, b4Σ−, 14Δ, 24Δ, 14Σ+, 16Σ+ and 16Π Λ-S states and the PECs of 16 Ω states generated from the eight bound Λ-S states of PO radical. All the PECs are calculated by the CASSCF method, which is followed by the internally contracted MRCI approach with the Davidson modification. The spin-orbit coupling is included by the state interaction approach with the Breit-Pauli Hamiltonian. The convergent behavior is observed and discussed with respect to the correlation-consistent basis set and level of theory. The effect on the energy splitting by core-electron correlations is studied. To improve the quality of PECs, core-valence correlation corrections are included by a cc-pCVTZ basis set. Scalar relativistic correction calculations are made by the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. All the PECs are extrapolated to the complete basis set limit. With these PECs, the spectroscopic parameters of 10 Λ-S and 16 Ω bound states are evaluated. The vibrational manifolds of the first 16 vibrational states are evaluated for each Λ-S and Ω state of non-rotation radical. With the PECs obtained by the MRCI+Q/CV+DK+56+SO calculations, the SO coupling splitting energy of X2Π Λ-S state is determined as 225.18 cm−1, which agrees well with the measurements of 224.17 cm−1. Moreover, other spectroscopic parameters and molecular constants calculated here are also in excellent agreement with the available measurements. It shows that the spectroscopic parameters and molecular constants reported here can be expected to be reliable predicted ones.

► Convergent behavior is observed with respect to the basis set and level of theory. ► Effect on the PECs by core-valence correlation and relativistic corrections is included. ► PECs are extrapolated to the CBS limit. ► Effect on the spectroscopic parameters by the SO coupling is discussed. ► Spectroscopic parameters of 10 Λ-S and 16 Ω states are obtained.