Ab initio calculations on spectroscopic and transition properties of NaHe including spin-orbit coupling

Abstract

The interactions between alkali-metal atoms and rare-gas atoms have attracted much theoretical and experimental research interest. And accurate spectroscopic parameters play a crucial role in understanding the bond components of the interatomic potentials. In this study, the high-level ab initio calculations on the Rydberg states of NaHe correlating with the lowest seven dissociation limits are performed by utilizing the coupled-cluster method with all-electron Gaussian basis sets. The open-shell coupled cluster method restricted to single, double, and noniterative triple excitations (RCCSD(T)) was used to computed the potential energy curves (PECs) of ground state of NaHe. Subsequently, open-shell equation-of-motion coupled-cluster method limited to singly and doubly excited (EOM-CCSD) is utilized to compute the excitation energies. The spin-orbit coupling (SOC) is introduced with Breit-Pauli operator via state-interacting technique, in which the SOC elements were computed with complete active space self-consistent field (CASSCF) wavefunctions. Based on the computed PECs of the Λ–S and Ω states, the spectroscopic constants of the bound states of NaHe are determined. The vertical transition properties from the bound Rydberg states are also investigated. The present work is helpful for spectroscopy and dynamics of weakly bound molecular systems in physics and chemistry.