Zeeman splitting andgfactor of the1s22s22pP3∕22andP1∕22levels inAr13+

The Zeeman line components of the magnetic-dipole (M1) 1s{sup 2}2s{sup 2}2p {sup 2}P{sub 1/2}-{sup 2}P{sub 3/2} transition in boronlike Ar{sup 13+} 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{sub 1/2}=0.663(7) and g{sub 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.