Accurate spectroscopic constants of the lowest two electronic states in S2 molecule with explicitly correlated method**Project supported by the National Natural Science Foundation of China (Grand No. 11574114) and the Natural Science Foundation of Jilin Province, China (Grand No. 20150101003JC).

Abstract

A computational scheme for accurate spectroscopic constants was presented in this work and applied to the lowest two electronic states of sulfur dimer. A high-level ab initio calculation utilizing explicitly correlated multireference configuration interaction method (MRCI-F12) was performed to compute the potential energy curves (PECs) of the ground triplet and first excited singlet a1Δg states of sulfur dimer with cc-pCVXZ-F12(X = T, Q) basis sets. The effects of Davidson modification, core–valence correlation correction, and scalar relativistic correction on the spectroscopic constants were examined. The vibration–rotation spectra of the two electronic states were provided. Our computational results show excellent agreement with existing available experimental values, and the errors of main spectroscopic constants are within 0.1% order of magnitude. The present computational scheme is cheap and accurate, which is expected for extensive investigations on the potential energy curves or surfaces of other molecular systems.