Dissociation energies of the hydrogen and deuterium molecules.

Abstract

Fluorescence-excitation spectroscopy near \ensuremath{\sim}84 nm has been used to measure the threshold for the dissociation of ${\mathrm{H}}_{2}$(B' $^{1}\mathrm{\ensuremath{\Sigma}}_{\mathit{u}}^{+}$)=H(1s)+H(2s) at 118 377.06\ifmmode\pm\else\textpm\fi{}0.04 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and the corresponding limit for ${\mathrm{D}}_{2}$ at 119 029.72\ifmmode\pm\else\textpm\fi{}0.04 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The onset of dissociation was observed clearly, free from overlapping molecular lines, by the use of delayed quenching of 2s atoms produced by the photoexcitation pulse. These measurements have yielded the values ${\mathit{D}}_{0}$(${\mathrm{H}}_{2}$)=36 118.11\ifmmode\pm\else\textpm\fi{}0.08 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and ${\mathit{D}}_{0}$(${\mathrm{D}}_{2}$)=36 748.38\ifmmode\pm\else\textpm\fi{}0.07 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for the dissociation energies of the ground electronic states X $^{1}\mathrm{\ensuremath{\Sigma}}_{\mathrm{g}}^{+}$, in agreement with the latest ab initio calculations, which include nonadiabatic, relativistic, and radiative corrections. From the present values and recently determined ionization energies of ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$, the dissociation energies of the respective ions were found to be ${\mathit{D}}_{0}$(${\mathrm{H}}_{2}^{+}$)=21 379.37\ifmmode\pm\else\textpm\fi{}0.08 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and ${\mathit{D}}_{0}$(${\mathrm{D}}_{2}^{+}$)=21 711.64\ifmmode\pm\else\textpm\fi{}0.07 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, also in agreement with recent ab initio calculations.