Magnetic Moment of the Proton in H2O in Bohr Magnetons

We have measured the ratio of the electron g-factor in hydrogen to the proton g-factor in a spherical sample of H2O by comparing the electron spin frequency, as measured with a hydrogen maser, to the proton spin flip frequency, as measured by NMR. The result is gj(H)/gṕ = 658.216 0091(69) 10 parts per billion (ppb) at a temperature of 34.7°C. This yields a value for the proton moment in Bohr magnetons of μṕ/μB = 0.001 520 992 983(17) (11 ppb). Our result differs from the best previous value by 150 ppb.