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The Raman spectra of pyridine adsorbed on a number of metal oxide surfaces are used to distinguish between physical and chemical adsorption, and to indicate the nature of the bonding of pyridine to these surfaces. SO9 5NH, HantsBEFORE 1967 there were only two sets of papers relating to the study of adsorbed species by Raman spectroscopy l4 although i.r. absorption was widely used.6'6 Pershina and Raskin were able to obtain many useful data, but the experiment was then relatively difficult. The continuous gas laser as an excitation source for Raman spectroscopy, together with more sophisticated instrumentation , has made possible the wider application of Raman spectroscopy, and it can readily be used to study surface-adsorbed species.&S Pyridine has been widely used in the i.r. study lo of the nature of active sites on the surface of catalysts. Some absorption bands in the pyridine spectrum are sensitive to the environment of the molecule, so that the i.r. spectrum of pyridine adsorbed on a surface can dis-

Oxygen-oxygen stretching frequencies for peroxides and superoxides of Group IA and IIA elements are presented and their relationship to bond orders discussed.EXPERIMENTAL factors, particularly in cases of coloured, photosensitive, or insoluble species, have limited the versatility of the Raman method. The advent of laser sources has now largely removed such limitations. In symmetrical molecules vibrational modes in which 8p/ 2q (p = dipole moment, q = normal co-ordinate) is zero are not active in absorption but frequently give rise to prominent features in the Raman spectrum.We have studied the oxygen-oxygen stretching frequencies in the peroxides and superoxides of the metals of Groups IA and IIA. X-Ray crystallography has established that both these types of oxide contain discrete "0," species and consideration of the stoicheiometry indicates that peroxides contain an 02ion, superoxides an 0,ion. A number of such peroxides and superoxides have been preparedl,, and examined with the Cary 81 Raman spectrometer powered by the helium-neon laser.

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