SKM 2023 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 27: Computational Biophysics II
BP 27.1: Vortrag
Donnerstag, 30. März 2023, 15:00–15:15, BAR 0106
Spectral signatures of excess-proton waiting and transfer-path dynamics — •Florian Brünig1, Manuel Rammler1, Ellen Adams2, Martina Havenith2, and Roland Netz1 — 1Freie Universität Berlin, Department of Physics, 14195 Berlin, Germany — 2Ruhr-Universität Bochum, Department of Physical Chemistry II, 44780 Bochum, Germany
Signatures of solvated excess protons in infrared difference absorption spectra, such as the continuum band between the water bend and stretch bands, have been experimentally known for a long time and have recently been used to analyze protonation dynamics in photoactive proteins. However, the theoretical basis for linking spectral signatures with the microscopic proton-transfer mechanism so far relied on normal-mode analysis.
We analyze the excess-proton dynamics in ab initio molecular-dynamics simulations of aqueous hydrochloric acid solutions by trajectory-decomposition techniques. The continuum band is shown to be due to normal-mode oscillations of temporary H3O+ complexes. The actual proton transfer between two water molecules, which for large water separations involves crossing of a barrier and thus is not a normal mode, is characterized by two time scales: Firstly, the waiting time for transfer to occur, which leads to a broad weak shoulder around 100 cm−1, consistent with our experimental THz spectra. Secondly, the mean duration of a transfer event, which produces a rather well-defined spectral contribution around 1200 cm−1 and agrees in location and width with previous experimental spectra.