Theoretical study on ten Λ-S states of Si2(-) anion: potential energy curves, spectroscopy and spin-orbit couplings.

The potential energy curves (PECs) of seventeen Ω states generated from the ten Λ-S states of the Si2(-) anion are studied in detail using an ab initio quantum chemical method for the first time. The PECs are calculated for internuclear separations from 0.10 to 1.20 nm by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson modification. The spin-orbit coupling is accounted for by the Breit-Pauli Hamiltonian. Core-valence correlation and scalar relativistic corrections are considered. Core-valence correlation corrections are included using an aug-cc-pCVTZ basis set. Scalar relativistic correction calculations are made with the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. Obvious effect of core-valence correlation corrections on the PECs is observed, in particular for the two lowest (2)Πu and (2)Σg(+) Λ-S states. All the PECs are extrapolated to the complete basis set limit. The lowest (2)Πu Λ-S state is found to be the ground state of Si2(-) anion. The convergence observations of present calculations are made and the convergent behavior is discussed with respect to the basis set and level of theory. The effects of core-electron correlations on the energy splitting are studied by the all-electron aug-cc-pCVTZ basis set. Using these PECs, the spectroscopic parameters of Λ-S and Ω states involved are determined. The vibrational manifolds are evaluated for each Λ-S and Ω state of non-rotation Si2(-) anion. It shows that the spectroscopic parameters and molecular constants of ten Λ-S and seventeen Ω states reported here can be expected to be reliable predicted ones.