Experimental Results on the Dynamic Polarisation in a Solid by Variation of Temperature

Abstract

A description of the apparatus for a new dynamic polarization effect by variation of temperature, and the experimental results obtained, are presented. As described earlier a temperature jump produces a very large enhancement of the dipolar signal (about 10.000) in solid y-picolene due to the dipolar couplings between the protons of the CH₃-group and the modes of the CH₃-rotator with the crystal phonons. A simple phenomenological model for the interpretation of the experimental data is introduced. Within the experimental errors agreement between model and data is obtained. From the shape of the measured polarization curves a dipolar polarization time T_p and the dipolar relaxation time T_d is determined. From the maxima of the polarization at different temperature jumps a curve dependent only on the temperature is constructed, which together with T_p and T_d characterizes completely the dynamic polarization behaviour. A comparison of the Zeeman- and dipolar relaxation with earlier measurements on similar molecules containing CH₃-groups shows that the CH₃-rotation in solid y-picolene is almost unhindered and that the "relaxation efficiency" is very low. These last conditions are important for a large enhancement of the dipolar polarization.