Theoretical study of the NaLi molecule: potential energy curves, spectroscopic constants, dipole moments and radiative lifetimes

Abstract

The adiabatic potential energy curves and the permanent and transition dipole moments of the low-lying electronic states of the NaLi molecule dissociating into Na(3s, 3p, 4s, 3d, 4p) + Li(2s, 2p, 3s, 3p, 3d) have been investigated. The molecular calculations are performed using an ab initio approach based on non-empirical pseudopotentials for Na+ and Li+ cores, parameterized l-dependent polarization potentials and full configuration interaction calculations through the CIPCI quantum chemistry package. The derived spectroscopic constants of the ground state and lower excited states are in good agreement with available experimental and theoretical works. However, the 7–101,3Σ+, 5–71Π, 2–63Π and 1–31,3Δ excited states are studied for the first time. The permanent dipole moment of NaLi has revealed both ionic characters relating to electron transfer and yielding Na+Li− and Na−Li+ arrangements. The transition dipole moment is used to evaluate the radiative lifetimes of the vibrational levels trapped in the 21Σ+ excited state for the first time. In addition to the bound–bound contribution, the bound-free term has been evaluated exactly using the Franck–Condon (FC) approximation and added to the total radiative lifetime.