Level isotope shifts of6,7Li

The isotope shift of the Doppler-free two-photon lines 2S-4S and 2S-3,4D in 6,7 Li have been measured with a thermionic diode. Because the 2S-3D and 2S-4D lines show, within the experimental uncertainty, the same residual transition isotope shift (transition isotope shift minus Bohr mass shift) the method recently proposed by Niemax and Pendrill (1980) could be applied to find the residual level isotope shifts of the ground state (2S) and the 4S level from the measured transition shifts. Taking into account all available experimental isotope line shift data of other authors the level shifts of some other lower levels in 6,7 Li are also given. The experimental values are in satisfactory agreement with specific mass shift data found by Martensson (1981) in ab initio Hartree-Fock calculations up to the second order.