Experimental Value ofΔEH−SHin Hydrogen

We have measured the $2{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}-2{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ separation, $\Delta E_{\mathrm{H}}-{\mathcal{S}}_{\mathrm{H}}$, in atomic hydrogen by an atomic-beam rf method. We find $\Delta E_{\mathrm{H}}-{\mathcal{S}}_{\mathrm{H}}=9911.213\mathrm{}\pm 0.058$ MHz. The quoted error is 1 average deviation from the mean for 115 line centers.