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 2Πu and 2Σg+ Λ–S states. All the PECs are extrapolated to the complete basis set limit. The lowest 2Πu 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.

Graphical abstractThe PECs of seventeen Ω states generated from ten Λ–S states of Si2- anion are studied in detail by the internally contracted MRCI + Q method. The SO coupling is included by the Breit–Pauli Hamiltonian using the ACVTZ basis set with 2s2p correlations. Core–valence correlation and scalar relativistic corrections are included. Core–valence correlation corrections are included by an ACVTZ basis set. Scalar relativistic correction calculations are made using the DKH3 approximation at the level of a cc-pV5Z basis set. Obvious effect of core–valence correlation corrections on the PECs is observed. All the PECs are extrapolated to the CBS limit. The lowest 2Πu Λ–S state is found to be the ground state. The convergent behavior is discussed with respect to the basis set and level of theory. The spectroscopic parameters of Λ–S and Ω states involved are determined. The vibrational manifolds are evaluated for each Λ–S and each Ω state of non-rotation anion. The SO coupling splitting energy of X2Πu Λ–S state is determined as 114.57 cm−1, which agrees well with the recent measurements of 115.29 cm−1. Other spectroscopic parameters and molecular constants are also in fair agreement with the measurements. It shows that the spectroscopic parameters and molecular constants reported in the present paper can be expected to be reliable predicted ones.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights►Effect of core–valence correlation and relativistic corrections on the PECs is included. ►Convergent behavior is observed with respect to the basis set and level of theory. ►SO coupling effect on the spectroscopic parameters is discussed. ►PECs obtained by the MRCI + Q are extrapolated to the CBS limit. ►Spectroscopic parameters of ten Λ–S and seventeen Ω states are obtained.