Protonenspinrelaxation von Benzol an Silikageloberflächen

Using spin-echo-techniques the temperature dependence of the proton magnetic relaxation times T₁ and T₂ of adsorbed benzene has been measured in the interval between +70 °C and —140 °C. Normal benzene C₆H₆ and mixtures of benzene and C₆D_6e were adsorbed on two sorts of silicagels which have been described elsewhere ^4,9.

The effective nuclear magnetic relaxation rates of adsorbed benzene are given by four contributions: the intramolecular proton-proton interaction, the interaction between benzene protons and paramagnetic impurities of the adsorbents, the interaction between benzene protons and hydroxyl protons on the silicagel surface, and the intermolecular interaction between benzene protons. These proton relaxation mechanisms depend differently on the H/D-ratio in C₆H₆—C₆D₆ mixtures (see section 4.1).

The temperature dependence of the contributions 1/T₁ intra and 1/T₂ intra due to intramolecular proton-proton interaction suggests an anisotropic rotation of benzene molecules on the gel used. Furthermore, the existence of three different regions for the adsorbed benzene molecules has been inferred (see sections 4.2 and 5).