Eur. Phys. J. D (2014) 68: 131
https://doi.org/10.1140/epjd/e2014-40411-6

Regular Article

Accurate calculations on the 12 electronic states and 23 Ω states of the SiBr⁺ cation: potential energy curves, spectroscopic parameters and spin-orbit coupling

College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, P.R. China

^a e-mail: scattering@sina.com.cn

Received: 13 July 2013
Received in final form: 22 October 2013
Published online: 22 May 2014

Abstract

The potential energy curves (PECs) of 23 Ω states generated from the 12 electronic states (X¹Σ⁺, 2¹Σ⁺, 1¹Σ⁻, 1¹Π, 2¹Π, 1¹Δ, 1³Σ⁺, 2³Σ⁺, 1³Σ⁻, a³Π, 2³Π and 1³Δ) are studied for the first time. All the states correlate to the first dissociation channel of the SiBr⁺ cation. Of these electronic states, the 2³Σ⁺ is the repulsive one without the spin-orbit coupling, whereas it becomes the bound one with the spin-orbit coupling added. On the one hand, without the spin-orbit coupling, the 1¹Π, 2¹Π and 2³Π are the rather weakly bound states, and only the 1¹Π state possesses the double well; on the other hand, with the spin-orbit coupling included, the a³Π and 1¹Π states possess the double well, and the 1³Σ⁺ and 1³Σ⁻ are the inverted states. The PECs are calculated by the CASSCF method, which is followed by the internally contracted MRCI approach with the Davidson modification. Scalar relativistic correction is calculated by the third-order Douglas-Kroll Hamiltonian approximation with a cc-pVTZ-DK basis set. Core-valence correlation correction is included with a cc-pCVTZ basis set. The spin-orbit coupling is accounted for by the state interaction method with the Breit-Pauli Hamiltonian using the all-electron aug-cc-pCVTZ basis set. All the PECs are extrapolated to the complete basis set limit. The variation with internuclear separation of the spin-orbit coupling constant is discussed in brief. The spectroscopic parameters are evaluated for the 11 bound electronic states and the 23 bound Ω states, and are compared with available measurements. Excellent agreement has been found between the present results and the experimental data. It demonstrates that the spectroscopic parameters reported here can be expected to be reliably predicted ones. The Franck-Condon factors and radiative lifetimes of the transitions from the a³Π_{0 +} and a³Π₁ states to the X¹Σ⁺₀₊ state are calculated for several low vibrational levels, and some brief discussion has been made.