Classical trajectory studies on the dynamics of one-photon double photionization of H$_2$O

Recent momentum imaging experiments at the Advanced Light Source have opened the possibility of measuring the complete triple differential cross section (TDCS) for one-photon double ionization of H$_2$O in the molecular frame. The measurements depend on the complete breakup process, H$_2$O $+ h\nu \rightarrow$ 2e$^-$+ H$^+$ + H$^+$ +O. At the 57 eV photon energy of the experiment this process could proceed via any of the nine energetically accessible electronic states of H$_2$O$^{++}$. To discover which ionization channels contribute to the observed TDCS for the electrons measured in coincidence with different kinetic energy releases, we have carried out classical trajectory studies for breakup of the water dication on all nine potential surfaces, sampling from a Wigner phase space distribution for the vibrational ground state of H$_2$O. The final momentum distributions of the protons and branching ratios between two- and three-body breakup are then analyzed and the results are compared with experiment to identify which ionization channels contribute to the TDCS observed in coincidence measurements of the ejected electrons.