Resonant photofragmentation of water at the oxygen K edge by high-resolution ion-yield spectroscopy

Resonant photofragmentation of core-excited water molecules has been studied with high-resolution partial-ion-yield spectroscopy. Both the single and coincidence channels were monitored simultaneously. A steep increase in the coincidence yield curves above the ionization threshold, where the normal Auger decay produces doubly charged or multiply charged species that yield two or more charged fragments, has been observed. By comparing the single and coincidence channels the relative weight of H neutral fragments has been qualitatively assessed, and found to be higher for the O $1\overrightarrow{s}{4a}_1$ primary excitation. The presented ion-yield data provide strong evidence for a branching between atomic Auger decay and molecular fragmentation in the ${\mathrm{O}}^{+}$ channel. The most unexpected result is the formation of ${\mathrm{H}}_2^{+}$ species being detected and attributed to a highly excited bending mode.