Redetermination of the Hyperfine Splittings of Hydrogen and Deuterium in the Ground State

The hyperfine splittings of hydrogen and deuterium in the $1{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ state have been remeasured by the atomic beam method. It is found that $\Delta \nu \left(\mathrm{H}\right)=(1420.40573\mathrm{}\pm 0.00005)\times {10}^6 invsec,$ $\Delta \nu \left(\mathrm{D}\right)=(327.384302\mathrm{}\pm 0.000030)\times {10}^6 invsec.$ The result for hydrogen is in agreement with a recent measurement of Wittke and Dicke. It is significant disagreement with an earlier atomic beam measurement.