Abstract
A new approach to investigating the double layer properties at electrode surfaces is introduced by comparing in situ and ex situ infrared reflection absorption spectroscopic (IRAS) results of a system prepared under the same experimental conditions. Cyanide adlayers on a Pt(111) electrode have been investigated in cyanide free 0.1 M KCl solution showing one single bipolar band around 2100 cm −1 and a Stark shift of 21 cm −1/V. This low tuning rate is explained by coadsorption of chloride in the cyanide adlayer, which results in a lower local electric field effective in the double layer. After transfer to ultrahigh vacuum (UHV) the system has also been investigated by ex situ IRAS, low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). LEED pictures show two different adlayer structures depending on the emersion potential. After emersion at anodic potentials the well-known (2 3 ×2 3 )R30°-CN structure is detected, whereas at cathodic potentials a (2×2)-CN structure could be observed. The related Fourier transform infrared (FTIR) spectra display a similar single band near 2110 cm −1 as in situ, with a clear dependence on the emersion potential, indicating a successful transfer to UHV. Therefore with ex situ IR spectroscopy the influence of the emersion potential on the CN stretching vibration could be directly compared with the in situ measurements.
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