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Dynamical and structural properties of linear water Clusters: Long range Proton Transport in an ordered Water Phase

Final Activity Report Summary - VENDRELL_TC_06 (Dynamical and Structural Properties of Linear Water Clusters: Long Range Proton Transport in an Ordered Water Phase)

We have studied in full quantum-dynamical detail the protonated water dimer, which is the smallest water cluster in which a proton is shared by two water molecules. Protonated water clusters play a very important role as charge carriers in liquid water, as well as in biological environment. Thanks to recent advances in laser technology, very accurate vibrational spectra for this kind of systems have become available during the last years. Such spectra could not be assigned by standard methods of vibrational analysis, due to the large amplitude motions and floppiness of the cation caused by the soft interatomic potential governing the motion of the atoms.

In a set of works, which have involved important methodological developments in the field of quantum dynamical studies of molecular vibrations, we have been able to explain the experimental spectra, and so we have been able to understand much better the structure and dynamics of the hydrated proton. Our studies reveal that the motions of the shared proton are coupled to vibrations of the whole cluster, which causes ultrafast vibrational energy dissipation. In full quantum-mechanical simulations of the proton transfer event between two water molecules, we have shown that the energy involved in the proton transfer is dissipated to the vibrations of the whole complex in less than 300 femtoseconds. This implies that coherent proton transfer over a large chain of water molecules is highly unlikely, and that the activation for multiple proton transfer processes along chains has to be of thermal nature. Such studies set the bases to be taken into account, if chains of water molecules are to be used as long range proton carriers in technological applications.