Laser Raman spectra of adsorbed species

Abstract

Experimental methods for recording laser Raman spectra of molecular species adsorbed on high surface area substrates are described. The origin of the spectra is discussed; they definitely originate from vibrations of the surface adsorbed species. Spectra of a range of adsorbates including halogens, hydrocarbons and halogenated hydrocarbons, nitriles and aldehydes adsorbed on a range of oxide surfaces are discussed. The spectra closely resemble those of the liquid if physical adsorption is involved, but considerable frequency and intensity changes occur if the molecules are chemisorbed. Raman spectroscopy has an advantage over infra-red in this field in that bands due to these adsorbents are not prominent in the spectrum. However, the method lacks sensitivity as yet and is restricted to good Raman scatterers adsorbed on high surface area adsorbents.