Dresden 2003 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 21: POSTER B

CPP 21.14: Poster

Dienstag, 25. März 2003, 19:00–21:00, ZEU/250

2D vibrational spectroscopy study on self trapping of the amide-I mode of acetanilide — •Julian Edler and Peter Hamm — Physikalisch Chemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH 8057 Zürich, Switzerland

Acetanilide (ACN), a molecular crystal consisting of hydrogen bonded peptide units, is a simple model system to study vibrational excitations in proteins. The absorption spectrum of the amide-I band exhibits an anomalous double peak structure. Different previous explanations for the underlying mechanism of this doublet include self trapping, a Fermi resonance and conformational substates.

We use two dimensional vibrational (2D) spectroscopy to clarify the origin of this band. By comparing the 2D spectrum of ACN with both that of a typical Fermi resonance and that of a system with two conformational substates, it is shown that these two mechanisms cannot account for the ACN spectrum. On the other hand, self trapping of the amide-I band, which is mediated through the hydrogen bonds that stabilize the crystal structure, can naturally explain the 2D response.