A Molecular Motor

Abstract

Experiments are described in which the rotation of methyl groups in solids at helium temperatures is driven using external magnetic fields. The orientation of the nuclear magnetic dipoles is caused to oscillate in synchronism with coherent tunnelling rotation, switching time-dependent internal-magnetic-field gradients due to the dipole-dipole interaction to produce a small steady torque. The resulting change in the frequency of tunnelling, of the order of 150 kHz, is detected by field cycling NMR.