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Electron diffraction self imaging of molecular fragmentation in two step double ionization of water

We doubly ionize H2O by single photon absorption at 43 eV leading to H+ + OH+. A direct double ionization and a sequential process in which single ionization is followed by rapid dissociation into a proton and an autoionizing OH- are identified. We obtain information about the internuclear distance at which the decay of the OH- occurs from the angular distribution of the autoionization electron.

Figure 1. Angular distribution of the autionization electron, relative to the proton direction. Black dots are experimental data, red line simulation for an internuclear distance of 800 a.u..

The autoionization electron shows a preferred emission in the direction of the proton. This anisotropy can be reproduced almost exactly with a simple classical scattering simulation where one Coulomb potential is located at origin and another one at a distance R simulating the proton. The electrons are launched radially from a sphere of 1 a.u. around the origin. Using R as a fitting parameter we obtain an internuclear distance of 800 a.u. at which the autoionization occurs. This corresponds to a decay time of approximately 2 ps.