Infrared Study of Adsorbed Molecules on Metal Surfaces by Reflection Techniques

Abstract

The problem of obtaining the infrared spectrum of a molecular monolayer adsorbed on a bulk metal is discussed. The intensity of an infrared absorption band in radiation reflected from the surface is calculated for (a) various optical constants of the adsorbed layer and the metal, (b) various thicknesses of the adsorbed layer, (c) various angles of incidence, and (d) both states of polarization of the incident radiation. The absorption factor for infrared radiation polarized parallel to the plane of incidence typically has a peak at an incident angle of about 88°, where the absorption is 5000 times greater than at normal incidence. The absorption of a thin layer by the reflection technique, at optimum conditions, is calculated to be about 25 times greater than by transmission through the unsupported film at normal incidence.

Infrared Reflection−Absorption Spectra of C2H4 and C2H6 on Cu: Effect of Surface Roughness

“…24 Furthermore, the intensity ratio of these bands for IRRAS to the corresponding ones in transmission on KBr can be explained by the classical theory and the typical IRRAS-enhancement factor. 1 The significant spectral difference between C 2 H 4 adsorbed on the two different Cu samples is the appearance of additional vibration modes already at low exposures to Cu(50K). These modes are exclusively Raman active for the free molecule, the a g (CH 2 scissor, R) mode at 1279 cm -1 and the a g (CC stretch, R) mode at 1542 cm -1 .…”

Film Growth of Ice by Vapor Deposition at 128−185 K Studied by Fourier Transform Infrared Reflection−Absorption Spectroscopy: Evolution of the OH Stretch and the Dangling Bond with Film Thickness

“…32 Furthermore, increasing the incident angle above 15°(toward more glancingangle incidence) significantly increases the intensity of the spectrum without affecting the general shape (Figures 2, curves F-K). 31 Evidently, the shape of the spectrum (determined predominantly by longitudinal excitations) is not particularly sensitive to the incident angle in the glancing incidence regime, and the experimental sampling angle (83°) used in the present work provides near optimal spectral intensity. The physics of reflection-absorption for a triple-medium system determines the dramatic differences in the σ-and π-polarized RA spectra for a wide range of film thicknesses.…”

“…In general, the film thickness can have a significant effect on the shape, frequency position and spectral intensity of the RA bands, and these effects have been discussed in detail by Greenler 31 and Decius and Hexter. 32 McIntyre and Aspens have used the Fresnel equations for reflection coefficients for paralleland perpendicular-polarized light to simulate the RA spectra of an absorbing dielectric film.…”

Disentangling Catalytic Activity at Terrace and Step Sites on Selectively Ru-Modified Well-Ordered Pt Surfaces Probed by CO Electro-oxidation

“…All experiments were made by employing a p-polarized radiation which allows to detect IR active species both at the electrode surface and dissolved into the thin layer, 47 according to the surface selection rule. 48,49 Electrode potentials were controlled by using a waveform generator (EG&G PARC 175) together with a potentiostat (Amel 551) and a digital recorder (eDAC ED 401). All the experiments were carried out at room temperature (25 o C).…”