Effect of a static electric field on the vibrational and electronic properties of a compressed CO adlayer on Pt(110) in nonaqueous electrolyte as probed by infrared reflection–absorption spectroscopy and infrared-visible sum-frequency generation spectroscopy

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Abstract
The CO–Pt(110) in nonaqueous electrolyteelectrochemical interface was studied by infrared reflection–absorption spectroscopy (IRAS) and infrared (IR)-visible sum-frequency generation (SFG) nonlinear vibrational spectroscopy over a wide range of applied potentials (−1.7⩽Φ⩽1 V/NHE). The integrated intensities of the IRAS and SFG peaks associated with resonant excitation of the atop CO internal stretch vibration (A IR and A SFG ) showed distinct variations with Φ. The influence of vibrational and electronic properties on the observed variations is discussed. Potential dependent dynamical charge transfer is not sufficient to explain the observed value of ∂A IR /∂Φ. It is shown that screening factors due to dipolar interactions between molecules within the compressed adsorbed layer must be taken into account in order to explain the variations of the IRAS and SFG data and that the observed behavior differences of A IR and A SFG with the potential are not necessarily related to changes in the Raman cross section of the adsorbate.