Experimental determination of the magnetic moment of the negative sulfur ion

We describe the measurement of the atomic g factor of the negative sulfur ion in the P322 ground state. This measurement uses a new technique for observation of microwave transitions in negative ions. Zeeman transitions in S-32 ions confined in a Penning trap are made observable through state-selective photodetachment. The magnetic field is measured by driving the cyclotron motion of electrons trapped in the same trap. The gJ factor is found to be 1.333 984(28).