Experimental ground stateg J-factor of Ba+ in a Penning ion trap

We observed the Zeeman-splitting of the 6S_1/2 – 6P_1/2 resonance transition of Ba⁺-ions (493.4 nm) in a 6T magnetic field. The ions were stored in a Penning quadrupole trap. We polarized the ground state by optical pumping and in a microwave-optical double resonance experiment we measured the ground state Zeeman-splitting. From the resonance frequency and the cyclotron frequency of electrons stored in the same trap we derived theg-factor of the 6S_1/2 state. The result isg_J(6S_1/2)=2.002 490 6(11), in reasonable agreement with recent calculations.