Zeeman splitting and g factor of the 1s22s22p 2P3/2 and 2P1/2 levels in Ar13+

The Zeeman line components of the magnetic-dipole (M1) 1s(2)2s(2)2p P-2(1/2)-P-2(3/2) transition in boronlike Ar13+ were experimentally resolved by high-precision emission spectroscopy using the Heidelberg electron beam ion trap. We determined the gyromagnetic (g) factors of the ground and first-excited levels to be g(1/2)=0.663(7) and g(3/2)=1.333(2), respectively. This corresponds to a measurement of the g factor of a relativistic electron in a bound non-S state of a multielectron ion with a 1.5 parts-per-thousand accuracy. The results are compared to theoretical calculations by means of the configuration interaction Dirac-Fock-Sturmian method including electron correlation effects and additional quantum electrodynamic corrections. Our measurements show that the classical Lande g factor formula is sufficiently accurate to the present level of accuracy in few-electron ions of medium nuclear charge number Z.