Dresden 2006 – scientific programme

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DY: Dynamik und Statistische Physik

DY 50: Lattice Dynamics and Non-Linear Excitations

DY 50.4: Talk

Friday, March 31, 2006, 11:00–11:15, H\"UL 186

Raman spectroscopy studies on THF clathrate hydrates — •Beata Walasek, Sascha Eschborn, and Rudolf Feile — Institut für Festkörperphysik, Technische Universität Darmstadt, Hochschulstr. 8, 64289 Darmstadt

Clathrate hydrates consist of an ice-like tetrahedral network of hydrogen bonded water molecules, forming polyhedral cages in which various guest molecules can be enclosed. The host lattice is stabilised by van der Waals interaction between guest and water molecules.

We investigate the interaction of tetrahydrofurane (THF) molecules with the host water cage comparing THF molecular vibrations in pure THF with those of THF molecules in the neighbourhood of either water molecules in liquid water or water molecules forming the clathrate cages. Raman spectra of aqueous and deuterated water solutions of THF were recorded from 500 cm^-1 to 3500 cm^-1 The strongest influence of the THF-water interaction is observed for the ring breathing mode (C-C-C-C stretches) and C-O-C stretch mode around 920 cm-1. In pure THF both vibrational modes have almost the same frequency. The interaction (hydrogen bonding) with H_2O/D_2O shifts the C-O-C mode in liquid water. On formation of the clathrate both vibrations have almost the same frequency again, showing that the hydrogen bonds of the THF molecule to neighboring H_2O/D_2O molecules are strongly weakened in the clathrate.

Below 120 K a splitting of the two modes set in. This may reflect either structural changes in the host lattice or the freezing of the THF molecule into inequivalent orientations within the cage.