Introduction
Reflection Adsorption Infrared Spectroscopy (RAIRS) offers a means of probing vibrations at surfaces with high resolution and, with its ease of implementation and strict selection rules, is a convenient technique for verifying molecular integrity and orientation at metal surfaces. The ability of RAIRS to identify surface species, when combined with the quantitative attributes of Low Energy Electron Diffraction (LEED), results in a powerful tool for surface structure determination. Its insensitivity to ambient gas pressures also makes RAIRS ideal for studying catalytic reactions under a wide range of pressure conditions.
The maturity of RAIRS as a standard surface analytical technique is exemplified by the results that have emerged from our laboratories over the past decade. Our focus of attention from the early use of RAIRS as a simple structural characterisation tool to characterise simple diatomic molecules such as CO and NO on low Miller index crystal planes, to its present application in the general exploration of several important themes in the surface vibrational spectroscopy of the identification of novel surface intermediates, the determination of adsorbate bonding geometries, the elucidation of surface reaction pathways in catalytic reactions, and studies on metal-supported thin oxide films.
Our RAIRS Apparatus
Two ultra-high vacuum (UHV) chambers are currently being used for RAIRS studies of molecular adsorption and catalysis on metal single crystal surfaces. Both systems have standard facilities for sample cleaning and characterisation using LEED, Auger Electron Spectroscopy (AES), and Temperature-programmed Desorption Spectroscopy (TDS). One of our UHV systems has a novel transfer mechanism that allows efficient sample transport between the UHV system and a coupled infrared cell that can be isolated and pressurised to 1 atmosphere. The second RAIRS system is dedicated to UHV experiments, and is currently being equipped with a simple thermal molecular beam that will allow measurement of sticking probabilities (and hence coverage) and the characterisation of reaction products from the surface alone.