Chapter 2: Isotopes in the FTIR investigations of solid surfaces

In this chapter the recent achievements in the use of isotopically labelled molecules for characterization of surfaces by FTIR and other vibrational spectroscopy techniques is reviewed. A brief theoretical background is provided where special attention is paid on the deviations of the experimental results from the theory. Then the application of D-, ¹³C-, ¹⁵N- and ¹⁸O-labelling is consecutively considered. For deuterium we first discuss the properties of surface OD groups and then the use of deuterated molecular probes (D₂, CHD₂OH, C₂D₅OH, C₆D₁₂). When describing ¹³C-labelled compounds the application of ¹³CO and ¹³C¹⁸O is compared and then other labelled compounds (¹³CO₂, D¹³CN, ¹³CH₃OH, etc.) are considered. In the next section ¹⁵N₂, NO isotopologues, (¹⁵NH₂)₂CO and aminoacids are discussed. For ¹⁸O-labelling we first consider the use of surfaces enriched to ¹⁸O, then different O₂ adsorption and finally, H₂¹⁸O and C¹⁸O. In all cases the application of isotopic labelling for clarifying the mechanisms of catalytic reactions is also considered.