Accurate calculations of the 18 Λ-S states and 50 Ω states of PO⁺ cation: potential energy curves and spectroscopic parameters including the spin-orbit coupling effect

Abstract

The potential energy curves (PECs) of 5 Ω states generated from the 18 Λ-S states (X ¹ Σ ⁺, A¹Σ⁻, 1¹ Δ, 1¹ Π, 2¹Σ⁺, 2¹ Π, a ³ Σ ⁺, 1³ Δ, 1³ Π, 1³Σ⁻, 2³Σ⁺, 2³ Π, 1⁵Σ⁺, 1⁵ Π 2⁵ Π, 1⁵Σ⁻, 2⁵Σ⁺ and 1⁵ Δ) of PO⁺ cation are studied for the first time for internuclear separations from about 0.08 to 1.0 nm. Of these Λ-S states, only the 2⁵Σ⁺ and 1⁵ Δ are the replusive ones. The a ³ Σ ⁺, 2³Σ⁺, 1⁵Σ⁻, 2³ Π, 1³ Δ, 2⁵Σ⁺ , and 1⁵ Δ are the inverted states with the spin-orbit coupling effect included. The 1¹ Π, 1³ Π, 1⁵ Π and 2³ Π states possess the double well. The 1⁵Σ⁻, 2¹ Π and 2⁵ Π states and the second wells of 1¹ Π, 1³ Π, 2³ Π and 1⁵ Π states are the rather weakly bound states. The PEC calculations are performed by the CASSCF method, which is followed by the icMRCI approach with Davidson correction in combination with the aug-cc-pV6Z basis set. Core-valence correlation and scalar relativistic corrections are included at the same time. The spin-orbit coupling effect is accounted for. All the PECs are extrapolated to the complete basis set limit. The spectroscopic parameters are evaluated for all the Λ-S and Ω bound states, and compared with the measurements and other theoretical results. Fair agreement is found between the present spectroscopic parameters and the measurements. The vibrational properties are evaluated for the weakly bound states. The effect of spin-orbit coupling on the spectroscopic parameters is discussed. The results reported in this paper can be expected to be reliable predicted ones.