Hannover 2010 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

MO: Fachverband Molekülphysik

MO 15: Photochemistry II

MO 15.1: Vortrag

Mittwoch, 10. März 2010, 14:00–14:15, F 142

Vibrational dynamics of the OH stretching mode in aqueous hydrates — •Stanislav Pandelov, Jasper Werhahn, Alfred Laubereau, and Hristo Iglev — Physik-Department E11, Technische Universität München, D-85748 Garching, Germany

Solid hydrates of salts containing a fixed ratio of water molecules in their crystal structures have attracted special interest due to their importance in geology, chemistry, and physics. The quest for deciphering the properties of hydrogen bonds makes those materials ideal candidates for studying the spectral signatures of water in different, well-defined environments with varying bonding partners and distances. We report on the first time-resolved study of the OH stretching vibration in NaCl dihydrate with the use of two-color IR spectroscopy. The water molecules bound in the hydrate show two well separated absorption bands at 3426 cm⁻¹ and 3541 cm⁻¹. The transient data display an ultrafast heating of the polycrystalline ice-hydrate samples after excitation of the OH stretching vibration and its transient relaxation. The relaxation time of the low-frequency OH stretching band in the NaCl hydrate is measured to be 6.8± 1ps. The dynamics are significantly slower than those measured in neat water. This fact, together with the reproducible crystalline environment reveals the potential of aqueous hydrates for a systematic investigation of the OH stretching vibration in varying hydrogen bonding environments. An expansion of the investigation to other hydrates will offer new insights into the physics underlying the detection of hydrogen bonded systems via the OH group and should be pursued experimentally and theoretically.