Deuterium atomic mass from Fourier-transform–ion-cyclotron-resonance measurement of the mass difference between ${}_{}{}^1{}_{}{}^{}\mathrm{H}_2^{}{}_{}{}^{}$${\mathrm{O}}^{+}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{HO}_{}^{+}{}_{}{}^{}$

The mass difference, ${\mathit{m}}^1$${\mathrm{H}}_2$${\mathrm{O}}^{+}$-${\mathit{m}}^2$${\mathrm{HO}}^{+}$=0.001 548 296(12), corresponding to a mass-ratio precision of 6×${10}^{\mathrm{-}10}$, has been determined by Fourier-transform ion-cyclotron-resonance (FT ICR) mass spectrometry. Three related results are calculated from that mass difference: 2${\mathit{m}}^1$H-${\mathit{m}}^2$H=0.001 548 302(12) u; mass of the deuterium atom, 2.014 101 764(13) u; and deuteron binding energy, ${\mathit{S}}_{\mathit{n}}$${(}^2$H)=2 388 183(14) nu [=2 224 579(13) eV, in which 1 u=931.494 32(28) MeV]. In all three cases, the FT ICR mass-spectrometry-derived value improves significantly the precision of prior measured or recommended values.