Study of utraslow atomic motions by magnetic resonance

Magnetic resonance has been widely used to study phenomena such as atomic diffusion and molecular reorientation. It is applicable when the mean time, r, between atomic jumps is either (a) sufficiently short to narrow the resonance line width or (b) of the correct magnitude to produce spin-lattice relaxation. Case (a) occurs when r is less than 1/Aco where Au> is the rigid lattice linewidth. Case (b) occurs when T is of the order of l/co0 , where oo0 is the Larmor frequency. Typically, case (a) is found when r < 100 /isec, case (b) when r ~ 10 ~ 8 sec. In this Letter we report a new, experimentally simple technique which enables us to study motions of a much slower rate, the criterion being roughly T < T 1 where T1 is the spin-lattice relaxation time.