NMR AND NQR SPIN-LATTICE RELAXATION IN PARTIALLY DEUTERATED (NH4)2SNCL6

The chlorine-NQR and the deuteron-NMR relaxation have been investigate d in (NDxH4-x)2SnCI6 (x=0,0.4) in the temperature range 4-300 K. Besid es the large cross-relaxation maximum observed in both natural and par tially deuterated compounds at about 55 K the Cl-35-NQR relaxation rat e shows two smaller maxima at 20 and 30 K in the deuterated salt only. These maxima are shifted to a higher temperature for Cl-37 isotope. T he peak at 30 K has a corresponding tunneling channel in the 2D-NMR re laxation rate. Deuteron spin-lattice relaxation rates, measured at 13. 86 and 52.37 MHz, besides the level-crossing maxima, also show classic al maxima related to molecular motions against a barrier about 15% of the full potential. All these effects are caused by limited jumps in a substructure at the bottom of the potential.