Calculations of specific mass shifts in Li+(1s2) and Li(1s22s, 1s22p)

A multiconfigurational calculation with the electron states expanded in a basis of Gaussian functions has been performed to give values of the specific mass shift ( 7 Li- 6 Li) as follows: Li + (1s 2 ), 25.077 GHz; Li(1s 2 2s), 26.165 GHz; Li(1s 2 2p), 21.557 GHz. Configuration interaction was taken into account by diagonalisation within a subspace consisting of functions with s-, p- and d-type symmetry. The size and quality of the basis are discussed; it is shown that with an even-tempered basis, the calculated specific mass shift tends to a constant value as the basis is expanded. The results are compared with those of other theoretical methods and with experimental data.