Hannover 2016 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 7: Femtosecond Spectroscopy 2

MO 7.7: Vortrag

Dienstag, 1. März 2016, 12:45–13:00, f102

Ultrafast Dynamics of Vibrational Relaxation of Pseudohalides in Liquid-to-Supercritical Water. A Critical Test of Fermi’s Golden Rule — •Jeannine Gleim, Denis Czurlok, Jörg Lindner, and Peter Vöhringer — Institut für Physikalische und Theoretische Chemie, Universität Bonn

In recent years, the vibrational spectroscopy of pseudohalide anions in condensed media has attracted much attention. They were studied in the context of dynamical solute-solvent interactions and vibrational energy relaxation (VER) in hydrogen-bonded liquids like water.

Here, the stretching vibration of ¹⁵N-labelled thiocyanate, selenocyanate and azide anions in aqueous solution were studied with Fourier-Transform IR-spectroscopy (FTIR) as well as femtosecond IR-pump-probe spectroscopy (fs-IR-PP). All experiments were carried out under isobaric conditions at a pressure of 500 bar over a wide temperature range covering the liquid and supercritical phases of water.

Relaxation rate constants were determined from the decay of the v=1 excited state absorption. In all studied cases, the temperature dependencies of the relaxation rate constants are similar. However, the relaxation pathways differ. While the relaxation of thiocyanate and selenocyanate follow the VET pathway, that of azide follows a combination of both, the IVR and VET pathways. The results are interpreted in terms of Fermi’s Golden Rule and a resonant VET from the solute’s stretching mode to the combination tone of the bending and librational modes of water.