Mainz 2017 – scientific programme

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MO: Fachverband Molekülphysik

MO 15: Environment Controlled Processes

MO 15.6: Talk

Thursday, March 9, 2017, 15:45–16:00, N 6

An Experimental Test of Fermi's Golden Rule using Femtosecond IR Pump-Probe Spectroscopy — •Jeannine Gleim, Tobias Unruh, Denis Czurlok, Jörg Lindner, and Peter Vöhringer — Institut für Physikalische und Theoretische Chemie, Universität Bonn

Fermi's Golden Rule describes the coupling of an eigenstate of a quantum system with a resonant continuum of "background" states. In the context of vibrational energy relaxation in liquid solutions Fermi's Golden Rule (FGR) has never been tested rigorously through experimental studies. In the recent past, aqueous solutions of pseudohalide anions were used to study dynamical solute-solvent interactions and vibrational energy relaxation in hydrogen-bonded networks. Here, the cyanide stretching vibration of SC14N-, SC15N-, SeCN- and OCN- anions dissolved in water were studied with FTIR-spectroscopy as well as femtosecond IR-pump-probe spectroscopy. This solute vibration can couple resonantly to the continuum of bending-librational combination states of the liquid. All experiments were carried out under isobaric conditions at a pressure of 500 bar over a wide temperature range. T-dependent relaxation rates (k(VER)) were determined from the decay of the v = 1 excited state absorption. Furthermore, the T-dependent spectral overlap S(T) between the solute and solvent absorption bands were determined independently and were used as a measure of the density of "background" states that enters Fermi's Golden Rule. According to FGR, a linear relationship between S(T) and k(VER) exists which provides insight into the coupling strength of the solute and solvent.