Sum and Difference Frequency Generation at the Electrochemical Interface

Abstract

The surface electronic properties and the vibrational spectroscopy of the electrochemical interface are investigated by in situ Infrared‐Visible Sum (SFG) and Difference (DFG) Frequency Generation. We first present the theoretical background of SFG/DFG and their generation at the interface and calculate the interface second‐order susceptibility including the resonant contribution of the adsorbate and the non resonant contribution of the metal substrate electronic intraband and interband transitions. The effect of the latter is addressed by comparing the experimental SFG and DFG spectra recorded on silver, platinum and gold substrates. The experimental set‐up and procedure are then described, and some selected experimental examples are shown and discussed.

Sum Frequency Generation Study of CO Adsorption on Palladium Model Catalysts

“…For instance, SFG studies in electrochemistry have contributed to the understanding of the effect of the strong interfacial electric field onto the nature of the adsorbate/ metal (electrode) interaction [7][8][9]. Interference phenomena between the resonant signal from the adsorbed molecules and the nonresonant background occur [9][10][11] and, as a result, the line shape of the measured SFG signal can vary depending on the relative phase of both contributions.…”

“…Interference phenomena between the resonant signal from the adsorbed molecules and the nonresonant background occur [9][10][11] and, as a result, the line shape of the measured SFG signal can vary depending on the relative phase of both contributions. This effect is specifically relevant for metals, where the nonresonant signal strength can reach the same order of magnitude as the resonant term.…”

“…This effect is specifically relevant for metals, where the nonresonant signal strength can reach the same order of magnitude as the resonant term. Interesting surface properties, such as the point of zero charge for electrochemical interfaces, could be estimated by measuring the phase difference between the nonresonant and resonant contributions as a function of the applied potential [9]. Furthermore, the visible frequency and/or the SFG frequency may be resonant with electronic transitions of the substrate or the adsorbate.…”

“…Furthermore, the visible frequency and/or the SFG frequency may be resonant with electronic transitions of the substrate or the adsorbate. In this case, infrared/visible SFG, differently from linear techniques or SHG, allows one to probe simultaneously vibrational modes and electronic structure [9][10][11].…”

Sum-frequency generation as a vibrational and electronic probe of the electrochemical interface and thin films

“…The non-resonant background has a À90°p hase shift compared to the vibration modes. This is coherent with previous results [29] and related to the weak density of bound states lying below the onset of the interband transition of silver. In addition, the oscillator strength A 12 is positive whereas it is negative for A 18a .…”