ElectronicgFactor of Rubidium

Frequencies corresponding to Zeeman transitions in an optically pumped rubidium-87 sample have been measured relative to the free-precession frequency of protons in a spherical water sample. Observations were made at 12 and 6 G in a compensated solenoid. On the basis of accepted theory for the separation of energy levels in a magnetic field, the ratio of $g$ factors for rubidium electrons and protons was found to be 658.2323±0.0007. It follows that the electronic $g$ factor for rubidium is 25±1 parts per million higher than the $g$ factor for the electron in the hydrogen ground state. This result is combined with ratios of alkali $g$ factors measured in atomic beam experiments to give the $g$ factors for other alkalis.