Rostock 2019 – scientific programme
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MO: Fachverband Molekülphysik
MO 3: Ultrafast Processes in Solution
MO 3.2: Talk
Monday, March 11, 2019, 11:00–11:15, S HS 001 Biologie
Spectroscopic signatures of the dynamical hydration shell formation — •Henning Kirchberg1, Peter Nalbach2, and Michael Thorwart1 — 1Universität Hamburg, I. Institut für Theoretische Physik, Jungiusstr. 9, 20355 Hamburg — 2Westfälische Hochschule, Münsterstr. 265, 46397 Bocholt
The hydration shell, a specific formed water molecule network with hydrogen bonds near a solute, strongly influences the energetic and electronic properties of the solute and its (non-) solubility in a polar environment. The dynamical formation of a hydration shell is a process of central interest in many physical and chemical systems. We generalize the Onsager model of a static spherical cavity with a point dipole placed in a dielectric continuum solvent towards a dynamically varying Onsager sphere. In particular, we assume a dynamical growing layer of water around the central sphere. We calculate the response of the central molecular dipole to an external electric field in the presence of the dynamically growing layer. By this, we determine the energy cost for the solvation shell formation, which is responsible for the low solubility of hydrophobic agents in water. We find a frequency up-shift in the absorptive part of the response. Moreover, we are able to connect time-dependent spectroscopy signatures, i.e. the line width of the absorption spectrum, to dynamical time scales of the hydration shell formation and to the characteristic fluctuations of the structured water within the hydration shell.