Verschiebungen der magnetischen Kernresonanzsignale adsorbierter Moleküle

Abstract

Proton resonance shifts of molecules adsorbed on the surface of silicagels are investigated. In order to explain these shifts which are in the direction to higher fields (compared with the resonances of free liquids) the influence of paramagnetic impurities in the silicagel surface, the different diamagnetic volume susceptibilities, as well as the influence of the relaxation process and of bonding effects are discussed. It is pointed out that the observed resonance shifts are mainly caused by bonding effects in our case. An inhomogeneous broadening of the resonance lines (by a factor F up to 12), found by comparison with spinecho experiments, is shown to be correlated with the shifts. Using this fact the dependence of the factor F on the surface coverage can be explained qualitatively.