Metal surface, external reflection

The external reflection of infrared radiation can be used to characterize the thickness and orientation of adsorbates on metal surfaces. Buontempo and Rice [153-155] have recently extended this technique to molecules at dielectric surfaces, including Langmuir monolayers at the air-water interface. Analysis of the dichroic ratio, the ratio of reflectivity parallel to the plane of incidence (p-polarization) to that perpendicular to it (.r-polarization) allows evaluation of the molecular orientation in terms of a tilt angle and rotation around the backbone [153]. An example of the p-polarized reflection spectrum for stearyl alcohol is shown in Fig. IV-13. Unfortunately, quantitative analysis of the experimental measurements of the antisymmetric CH2 stretch for heneicosanol [153,155] stearly alcohol [154] and tetracosanoic [156] monolayers is made difflcult by the scatter in the IR peak heights. 

When the surfaces are highly reflecting as in the case of metals, external reflection spectroscopy (ERS) can be used with good success133). For optimum intensity of the reflection bands of thin films, angles of incidence near 88 are desirable. However, in order not to interfere with the incoming beam, angles of incidence near 80° are used. 

In the case of external reflectance at air-metal surfaces, the resultant standing E field has a contribution solely due to the z component of the p-polarized light the... 

For many years, IRRAS has been successfully applied to the study of thin films adsorbates on metal surfaces [36], In the case of monolayers deposited on metal surfaces, an IR external reflection spectrum is obtained by reflecting the incoming radiation from the three-phase ambient-adsorbate-substrate system, measuring the reflected intensity as a function of wavelength, and then ratioing... 

The increasing application of spectroscopic methods in electrochemistry has characterized the last decade and marked the beginning of new developments in electrochemical science [1]. Among these methods, in-situ infrared spectroscopy provides a very useful tool for characterizing the electrode-solution interface at a molecular level. First in-situ infrared (IR) electrochemical measurements were performed in 1966 [2] using the internal reflection form [3]. However, problems in obtaining very thin metal layers on the surface of the prisms used as IR windows, delayed the extensive application of in-situ IR spectroscopy until 1980, when the method was applied in the external reflection form [4]. The importance of this step does not need to be emphasized today. 

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