Neutral fragmentation of superexcited oxygen molecules

The mechanisms of neutral dissociation of oxygen molecules in the excitation energy range 15--25 eV have been studied in a dispersed fluorescence experiment. By detecting the fluorescence from excited oxygen atoms, we find that neutral superexcited ${\mathrm{O}}_{2}$ states below 20 eV dissociate into $\mathrm{O}(\mathrm{g}.\mathrm{s}.)+\mathrm{O}(3s,3p).$ At higher excitation energies $(\mathrm{h}\ensuremath{\nu}=20--25\mathrm{eV})$ the curve-crossing interactions following excitations to members of the Rydberg $c{}^{4}{\ensuremath{\Sigma}}_{u}^{\ensuremath{-}}$ series also yield atoms in Rydberg states $(nl,n>~4).$ The experimental data are analyzed on the ground of many-body perturbation theory, calculations which indicate the structure of the predissociating states converging to the experimentally observed ones.