Abstract. Experimental and theoretical investigations of the splitting of the hyperfme structure of the sodium and lithium-D-lines in magnetic fields between 0 and 1 T were performed. In this magnetic field region the fine structure levels J = t/2 and J = 3/2 of the excited term 2p begin to influence each other. In case of lithium crossings and anticrossings of hyperfine states stemming from different fine structure energy levels J = 1/2 and J = 3 / 2 can be observed. The measurements were performed by laseratomic-beam spectroscopy in dependence on the applied external magnetic field strength. The experimental spectra were compared with computed spectra. Spectra were simulated by calculations using for the hyperfine hamiltonian two hyperfine constants A and B in case of sodium and four hyperfine constants ac, ae, a0 and b in case of lithium. Values for this constants could be derived by fitting the theoretical splittings to the experimental ones. For the first time the gi -factor of sodium could be determined in a purely optical way.

Abstract. Using laser-atomic-beam spectroscopy and a highly precise lambdameter, we have determined the transition wavelengths of the lithium resonance lines to be: 6Li D,: 6707.0704 (5)

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