STRUCTURE AND PROPERTIES OF HYDROCARBON RADICAL CATIONS IN LOW-TEMPERATURE MATRICES AS STUDIED BY A COMBINATION OF EPR AND IR SPECTROSCOPY

Use of IR spectroscopy (as a supplement to EPR) may provide new insigh t into the problem of analysis of structure and properties of organic radical cations. In this work, the results of combined EPR/IR studies of the formation, structure and properties of hydrocarbon radical cati ons in halocarbon and solid rare gas matrices are discussed. Both IR a nd EPR studies were carried out with matrix deposited samples irradiat ed with fast electrons at 15 or 77 K. IR spectroscopic data were found to be helpful in three aspects: (i) characterization of the conformat ion and association and molecule-matrix interactions of the parent mol ecules; (ii) identification of diamagnetic products of the reactions o f radical cations in ground and excited states; (iii) determining the characteristics of vibrational spectra of the radical cations, which a re of primary interest for analysis of chemical bonding and reactivity of the radical cations. The applications of the combined approach are illustrated with examples of studies of several alkenes in Freon matr ices and alkanes in solid rare gas matrices. The matrix effects on tra pping and degradation of radical cations were interpreted as the resul t of variations in matrix electronic characteristics (IP, polarizabili ty) and molecule-matrix interactions.