Isotopic Labelling in Vibrational Spectroscopy: A Technique to Decipher the Structure of Surface Species

The purpose of this paper is to provide a clear and simple introduction to the application of isotopically labelled molecules in the characterization of various surfaces by vibrational spectroscopies. Although the possible applications are multifarious, we have tried to systematize the most important of them in several groups. Initially we provide a brief theoretical background on the effect of isotopic substitution on the vibrational spectra and then consider the practical application of the technique for establishing the structure and composition of surface species, determination of the origin of particular atoms in these species and obtaining details on the interaction between adsorbed molecules. The second part of the paper describes three purpose-designed surface studies exemplifying the use of isotopically labelled molecules in order to: (i) determine of the maximal number of CO molecules than can be simultaneously bound to one Na⁺ cation from the NaY zeolite; (ii) measure the dynamic and static shift of CO molecules adsorbed on Ru/ZrO₂; (iii) prove the H₂ dissociation on Ru/ZrO₂.