Calculations of 21 Λ-S and 42 Ω states of BC molecule: Potential energy curves, spectroscopic parameters and spin-orbit coupling effect

Abstract

The potential energy curves (PECs) were calculated for the 42 Ω states generated from the 21 Λ-S states (X4Σ−, A4Π, B4Σ−, a2Π, b2Σ−, c2Δ, d2Σ+, e2Π, 32Π, 42Π, 52Π, 22Σ−, 32Σ−, 22Σ+, 32Σ+, 22Δ, 32Δ, 14Σ+, 24Π, 14Δ and 12Φ), which originated from the lowest two dissociation channels, B(2Pu)+C(3Pg) and B(2Pu)+C(1Dg), of the BC molecule. The PECs were calculated for internuclear separations from 0.08 to 1.10nm using the CASSCF method, which was followed by the icMRCI approach with the aug-cc-pV6Z basis set. Of these 21 Λ-S states, the e2Π, 22Δ, 22Σ−, 42Π, 12Φ and 32Δ possess the double wells. The A4Π, a2Π, c2Δ, 24Π, 42Π, 52Π, 14Δ and 12Φ states are inverted with the spin-orbit coupling (SOC) effect taken into account. The first well of e2Π state and the second well of 42Π and 22Δ states do not have any vibrational states whether with or without the SOC effect included. All the Λ-S and Ω states involved in this paper are bound states. Scalar relativistic correction was included by the third-order Douglas–Kroll Hamiltonian approximation at the level of an aug-cc-pV5Z basis set. Core-valence correlation correction was included at the level of an aug-cc-pCV5Z basis set. The SOC effect was accounted for by the state interaction method with the Breit–Pauli Hamiltonian and the all-electron cc-pCV5Z basis set. The PECs of all the states were extrapolated to the complete basis set limit. The spectroscopic parameters were obtained. The vibrational properties of several Λ-S and Ω states with the relatively shallow wells were evaluated. The SOC effect on the spectroscopic parameters is not obvious for almost all the states. The spectroscopic properties reported in this paper can be expected to be reliably predicted ones.