An ESR Study of NO2 Adsorbed on Silica Gel Surfaces

NO2 adsorbed on silica-gel surfaces shows temperature-dependent ESR spectra, which can be explained by assuming a restricted rotation of the NO2 molecule, where the preferred axis is the O–O direction. It is concluded from this observation that a hydrogen-bond force between the oxygen of NO2 and OH groups on the silica-gel surfaces plays a part in the NO2-silica-gel interaction. It is also estimated, from the observed hyperfme tensor, that the ONO angle may become slightly smaller when NO2 is adsorbed onto the silica-gel surface from the gas phase.