Electron Spin Resonance Study of the Radiolysis of Monocarboxylic Acids Adsorbed on Silica Gel

Electron spin resonance measurements were carried out on γ-irradiated monocarboxylic acids (formic, acetic, and propionic acids) adsorbed on silica gel. In the case of formic acid, the spectrum assigned to the CO2− radical was mainly observed, but also observed was the signal caused by the defects of γ-irradiated silica gel, whereas for the acetic acid a quartet due to the methyl radical was obtained. These spectra, however, were not found in the frozen acids alone. As regards propionic acid, ethyl radicals were produced in both the adsorbed and frozen states. It was concluded from these results that the characteristic radiolysis of monocarboxylic acids on the adsorbed state is to be attributed to interaction between the acids adsorbed on silica gel as monomers and the surface. On the basis of these spectra, the adsorbed state of the acids and the stability of the radicals have been discussed.