AbstractThe products of the surface decomposition of NO2/N2O4on zeolites X and A and γ‐alumina have been investigated using Raman spectroscopy. On the zeolite surfaces results indicate that a self‐ionization surface reaction occurs to generate nitrate (NO3−) and nitrosonium (NO+) ions. The extent of self‐ionization of NO2/N2O4appears to be far greater for the zeolitic absorbed phase than for the liquid phase. The nitrate appears to be held on cation sites while the nitrosonium ion is associated with the zeolitic oxide framework. Two different nitrate species form on zeolite A while only one nitrate species was detected on zeolite X. In the zeolite systems the spectra of adsorbed NO+were resonance enhanced using shorter wavelength exciting lines while the nitrate spectra were conventional (spontaneous) Raman spectra. On γ‐alumina the products of the surface decomposition of NO2/N2O4consist of three distinct types of surface nitrate with NO+not bei