Non-Born-Oppenheimer dynamics of the photoionized Zundel cation: a quantum wavepacket and surface-hopping study.

The ultrafast fragmentation of the Zundel cation H(+)(H2O)2 after photoionization is studied by quantum-dynamics with the multiconfiguration time-dependent Hartree method and with surface-hopping approaches. A picture emerges in which the correlated motion of the electron hole and the shared proton leads to localization of the two positively charged entities at opposite sides of the Zundel dication in less than 10 fs followed by Coulomb explosion. Electronic non-adiabatic effects play a crucial role in the fragmentation dynamics. The photoionization spectrum of the cluster between 20 and 24 eV is calculated quantum-dynamically and its features explained. Two- and three-body fragmentation channels accessible by outer-valence ionization are also calculated and the branching ratios as a function of ionization energy are discussed. A good agreement between the quantum-dynamical treatment and surface-hopping is obtained for observables for which both methods are applied.