Improved Ionization and Dissociation Energies of the Deuterium Molecule

The ionization energy of D$_2$ has been determined experimentally from measurements involving two-photon Doppler-free vacuum-ultraviolet pulsed laser excitation and near-infrared continuous-wave laser excitation to yield $E_\mathrm{I}(\mathrm{D}_2)=124\,745.393\,739(26)$ \wn. From this value, the dissociation energy of D$_2$ is deduced to be $D_0$(D$_2$) = 36\,748.362\,282(26) \wn, representing a 25-fold improvement over previous values, and found in good agreement (at $1.6\sigma$) with recent ab initio calculations of the 4-particle nonadiabatic relativistic energy and of quantum-electrodynamic corrections up to order $m\alpha^6$. This result constitutes a test of quantum electrodynamics in the molecular domain, while a perspective is opened to determine nuclear charge radii from molecules.