AVS 49th International Symposium
    Electrochemistry and Fluid-Solid Interfaces Monday Sessions
       Session EC+SS-MoA

Paper EC+SS-MoA1
Femtosecond Spectroscopy at the Metal/Liquid Interface

Monday, November 4, 2002, 2:00 pm, Room C-104

Session: Liquid-Solid Interfaces & Nanoscale Electrochemistry
Presenter: A.W. Kleyn, Leiden University, The Netherlands
Authors: S. Roke, Leiden University, The Netherlands
M. Bonn, Leiden University, The Netherlands
A.W. Kleyn, Leiden University, The Netherlands
Correspondent: Click to Email
Vibrational sum frequency generation spectroscopy is an ideal technique to study molecules at surfaces and at buried interfaces with a high degree of molecular specificity. The most powerful feature of this technique is its capability to monitor intramolecular vibrations of the first layer of molecules on the surface: it essentially allows one to look inside the molecules at the interface. The use of femtosecond laser pulses allows one to not only perform frequency domain measurements, but also time domain measurements. We have performed femtosecond time and frequency domain measurements on the acetonitrile/gold interface. Comparison of the time and frequency domain results showed that, although the two approaches are in principle equivalent they are sensitive to different physical aspects of the system. Time domain measurements are more clearly influenced by the inhomogeneity of adsorption sites, whereas frequency domain measurements are more subject to the homogeneous features of the spectral line broadening. To account for this we have extended existing models for calculating SFG spectra and free induction decay measurements. From the combination of the measurements and our model we have obtained information on the orientation and binding of acetonitrile to the gold surface and determined the nature and time scale of the decay of the vibrational polarization of the CH and CN stretch vibrations. The CN oscillators are distributed inhomogeniously across the surface and have a dephasing time of 1.65 ps. The CH stretch vibration however does not feel the inhomogeneity and dephases 2.5 times faster (T2 = 610 fs), because the methyl groups are further away from the interface.