3D Imaging of the Collision-Induced Coulomb Fragmentation of Water Molecules

The multiple ionization and fragmentation of ${\mathrm{H}}_{2}\mathrm{O}$ by fast ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ ions was studied using a position- and time-sensitive multiparticle detector. By the coincident measurement of correlated fragment momenta a complete three-dimensional image of the breakup process can be obtained for each individual event. Of special interest is the process ${\mathrm{H}}_{2}\mathrm{O}\ensuremath{\rightarrow}{\mathrm{H}}^{+}+{\mathrm{H}}^{+}+{\mathrm{O}}^{+}$ where a simple Coulomb explosion model is insufficient to explain the measured fragmentation energies and angular correlations. Better agreement is achieved with ab initio multiconfiguration self-consistent field calculations of the intermediate ${\mathrm{H}}_{2}{\mathrm{O}}^{3+}$ parent ion.