Raman Spectroscopy of Adsorbates at Metal Surfaces

Abstract

Many of the important problems of applied significance in surface chemistry involve surfaces in contact with high pressure gases or with liquids or solids. These interfaces, which include catalyst surfaces under manufacturing conditions and electrochemical interfaces, cannot be studied directly by the high vacuum techniques of electron energy loss (EELS), Auger, or photoelectron spectroscopy, or by secondary ion mass spectrometry, and much interest has therefore recently been shown in developing Raman spectroscopy for surface molecular studies. This technique, which involves inelastic scattering of visible photons and is well known as a technique for vibrational spectroscopy in other fields, has several experimental features which make it particularly attractive for surface studies: (1) there are no limitations on the phase in contact with the surface other than that it is transparent to the incident and scattered photons. The ambient phase may therefore be a condensed phase or a gas, or vacuum; (2) the laser light source and spectrometer are external to the apparatus, the incident and scattered light entering and leaving the sample chamber through glass windows. The technique thus makes minimal demands on the design of the sample chamber; (3) the focussed laser beam provides microprobe capability; (4) the frequency resolution is good, being typically in the range 1–10 cm^‒1 depending on the slit width necessary for adequate signal/noise ratio.