Specific mass shift for thesup2Sground state of the lithium atom

The absolute specific mass shifts for the ²S ground state of the lithium atom are calculated using a 352-term Hylleraas-type wave function. The specific mass shifts for ⁷Li and ⁶Li are 5.180 and 6.042 cm^-1, respectively, using first-order perturbation theory, and 5.177 cm^-1 (⁷Li) and 6.039 cm^-1 (⁶Li) from a nonperturbative approach. With use of Pekeris's accurate values for the specific mass shifts of Li⁺, the transition isotope shift of Li relative to Li⁺ is calculated to be 1.101 GHz, using first-order perturbation theory, and 1.071 GHz from a nonperturbative procedure. The calculated shift is in very close agreement with the experimental value of 1.111±{}0.006 GHz obtained by Lorenzen and Niemax.