Ground- and excited stateg-factors of Ba+

We observed the Zeeman-splitting of the 6S 1/2-6P 1/2 resonance transition of Ba+ ions (493.4 nm) in a 6 T magnetic field. The ions were stored in a Penning quadrupole trap. From the splitting and the simultaneously measured cyclotron frequency of stored electrons we derived theg-factors of the 6S 1/2 and 6P 1/2 states. The results areg(6S 1/2)=2.00267(20) andg(6P 1/2)=0.66634(22).