Filters

2010 - 20142

More filters

20202
Reset filters

Settings

Subject: Protons × WGL Institute: MBI ×

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Competition between excited state proton and OH- transport via a short water wire: Solvent effects open the gate
    (London [u.a.] : Royal Society of Chemistry, 2014) Bekçioǧlu, G.; Allolio, C.; Ekimova, M.; Nibbering, E.T.J.; Sebastiani, D.
    We investigate the acid-base proton exchange reaction in a microsolvated bifunctional chromophore by means of quantum chemical calculations. The UV/vis spectroscopy shows that equilibrium of the keto-and enol-forms in the electronic ground state is shifted to the keto conformation in the excited state. A previously unknown mechanism involving a hydroxide ion transport along a short water wire is characterized energetically, which turns out to be competitive with the commonly assumed proton transport. Both mechanisms are shown to have a concerted character, as opposed to a step-wise mechanism. The alternative mechanism of a hydrogen atom transport is critically examined, and evidence for strong solvent dependence is presented. Specifically, we observe electrostatic destabilization of the corresponding πσ* state by the aqueous solvent. As a consequence, no conical intersections are found along the reaction pathway.
  • Thumbnail Image
    Item
    A cascaded laser acceleration scheme for the generation of spectrally controlled proton beams
    (College Park, MD : Institute of Physics Publishing, 2010) Pfotenhauer, S.M.; Jäckel, O.; Polz, J.; Steinke, S.; Schlenvoigt, H.-P.; Heymann, J.; Robinson, A.P.L.; Kaluza, M.C.
    We present a novel, cascaded acceleration scheme for the generation of spectrally controlled ion beams using a laser-based accelerator in a 'double-stage' setup. An MeV proton beam produced during a relativistic laser-plasma interaction on a thin foil target is spectrally shaped by a secondary laser-plasma interaction on a separate foil, reliably creating well-separated quasi-monoenergetic features in the energy spectrum. The observed modulations are fully explained by a one-dimensional (1D) model supported by numerical simulations. These findings demonstrate that laser acceleration can, in principle, be applied in an additive manner. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.