Double photoionization ofH2: An experimental test of electronic-correlation models in molecules

The double-photoionization cross sections of molecular hydrogen (${\mathrm{H}}_2$) and molecular deuterium (${\mathrm{D}}_2$) were measured by using the photoion-photoion coincidence method for photon energies ranging from the threshold energy around 50 eV up to, respectively, 140 and 98 eV. The comparison with the recent ab initio calculations of Le Rouzo [J. Phys. B 19, L677 (1986)] indicates that an important part of the double-photoionization process is accounted for by a rigorous description of the electron-electron interaction in the initial state. As a by-product of this work, it was also concluded that double photoionization of hydrogen can be considered as a vertical process and that Franck-Condon approximations are quite valid to calculate the kinetic energy of the resulting ${\mathrm{H}}^{+}$+${\mathrm{H}}^{+}$ fragments.