Dissociation energy of the hydrogen molecule

Fluoresence-excitation spectroscopy near 84.5 nm has been used to measure the threshold for the dissociation limit of ${\mathrm{H}}_2$(B’ ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$)=H(1s)+H(2s) at 118 377.06±0.04 ${\mathrm{cm}}^{\mathrm{-}1}$. This yields a value of ${\mathit{D}}_0$(${\mathrm{H}}_2$)=36 118.11±0.08 ${\mathrm{cm}}^{\mathrm{-}1}$ for the dissociation energy of the ground electronic state X${(}^1$ ${\mathrm{\Sigma }}_{\mathit{g}}^{+}$) of ${\mathrm{H}}_2$, in agreement with the latest theoretical calculation which includes nonadiabatic, relativistic, and radiative corrections. When combined with recent determinations of the ionization energy of ${\mathrm{H}}_2$ the present ${\mathit{D}}_0$(${\mathrm{H}}_2$) leads to the value ${\mathit{D}}_0$ ${\mathrm{H}}_2^{+}$)=21 379.36±0.08 ${\mathrm{cm}}^{\mathrm{-}1}$, also in good agreement with theoretical values.