Lower Rydberg 2D states of the lithium atom: Finite-nuclear-mass calculations with explicitly correlated Gaussian functions

Very accurate variational nonrelativistic calculations are performed for the five lowest Rydberg 2D states (1s2nd1, n=3,...,7) of the lithium atom (7Li). The finite-nuclear-mass approach is employed and the wave functions of the states are expanded in terms of all-electron explicitly correlated Gaussian function. Four thousand Gaussians are used for each state. The calculated relative energies of the states determined with respect to the 2S 1s22s1 ground state are systematically lower than the experimental values by about 2.5 cm-1. As this value is about the same as the difference between the experimental relative energy between 7Li+ and 7Li in their ground-state energy and the corresponding calculated nonrelativistic relative energy, we attribute it to the relativistic effects not included in the present calculations.