Ab initio configuration interaction study on the electronic structure of the 1–42Π states of SiO+ and the avoided crossings of the 2–42Π potential energy curves

Abstract

Ab initio configuration interaction (CI) calculations have been carried out to study the energetics and electronic structure of the 1–42Π states of SiO+ and the avoided crossings of the 2–42Π potential energy curves (PECs). Spectroscopic constant values are predicted for the experimentally unknown 2–42Π states. Two avoided crossings, one between the 2–32Π PECs and the other between the 3–42Π PECs, are found to have a marked characteristic of a small minimum energy difference between the relevant PECs; 0.12eV for the former and 0.04 eV for the latter. Each small minimum energy difference results principally from the lack of direct interaction between two main configuration state functions (CSFs) in the CI wavefunctions for the two 2Π states concerned, since the off-diagonal CI matrix element between the two main CSFs vanishes identically. The reasons for both the vanishing and the non-vanishing CI matrix elements in terms of the CSFs, which are important for the description of the two avoided crossings, are explained from the standpoints of the Slater-Condon rules and symmetry properties of the important CSFs. The main CSFs mix through the direct interactions with intermediary CSFs, representing the near-degeneracy effect resulting in the avoided crossing.