Nuclear Magnetic Resonance Experiment on Solid Hexamethyldisilane

抄録

Proton magnetic resonance of solid hexamethyldisilane was studied. Line width and spin-lattice relaxation time were measured in temperature range from liquid air to room temperature. By analysing these quantities following results were obtained: Even at liquid air temperature, each CH₃ group reorientates about its three-fold symmetry axis so rapidly as to narrow the dipolar width due to three proton interactions within itself (activation energy 2.6 kcal/mole). Then at about −120°C, reorientation of CH₃-groups about the axis joining two silicon atoms becomes rapid enough to narrow the width further (activation energy 5.7 kcal/mole). Spin-lattice relaxation time varies qualitatively in accordance with the above considered reorientational motions. At −51.3°C, this crystal changes its structure and at the same time rapid reorientational motion of the molecular axis is excited, resulting discontinuous decrease in the line width and discontinuous increase in the spin-lattice relaxation time. Above the transition temperature, self-diffusion of molecule as a whole starts and the line width decreases gradually to zero (activation energy 10 kcal/mole). No change in the line width was observed at the melting point.