Theoretical studies on 14 Λ-S and 30 Ω states of BeBr molecule: potential energy curves, spectroscopic parameters and spin–orbit couplings

Abstract

Using the complete active space self-consistent field (CASSCF) method followed by the internally contracted multi-reference configuration interaction (MRCI) approach in combination with the correlation-consistent basis sets, this paper studies the potential energy curves of X2Σ+, 22Σ+, 32Σ+, 12Σ−, A2Π, 22Π, 32Π, 12Δ, 14Σ+, 24Σ+, 14Σ−, 14Π, 24Π and 14Δ Λ-S states of BeBr molecule and the corresponding 30 Ω states for the first time. All the Λ-S states correlate to the first two dissociation channels, Be(1Sg) + Br(2Pu) and Be(3Pu) + Br(2Pu), of BeBr molecule. Of these Λ-S states, the 32Π and 24Π are found to be repulsive without the spin–orbit coupling, whereas 14Π, 24Π, 32Π and 24Σ+ are found to be repulsive with the spin–orbit coupling included. A2Π and 22Σ+ possess the double well whether the spin–orbit coupling effect is included or not. Only 14Σ+, 14Σ−, 12Π and 22Π are found to be the inverted Λ-S states. The spin–orbit coupling is accounted for by the state interaction approach with Breit–Pauli Hamiltonian using the all-electron cc-pCVTZ basis set. The potential energy curves determined by the internally contracted MRCI method are corrected for size-extensivity errors by means of the Davidson correction. Core–valence correlation correction is calculated with a cc-pCVTZ basis set. Scalar relativistic correction is included using the third-order Douglas–Kroll Hamiltonian approximation at the level of cc-pVTZ basis set. The spectroscopic parameters of all the Λ-S and Ω bound states are evaluated. The spectroscopic parameters are compared with those reported in the literature. Fair agreement is found between the present results and available measurements. In particular, the energy splitting of 204.43 cm−1 in the A2Π Λ-S state agrees well with the measurements of 201 cm−1. Analyses demonstrate that the spectroscopic parameters reported here can be expected to be reliably predicted ones.