1H NMR study of proton dynamics in (NH4)3H(SO4)2

Proton diffusion in the superprotonic phase of [(NH4)1−xRbx]3H(SO4)2 as studied by 1H spin-lattice relaxation

“…in the temperature region around the phase transition, together with those of (NH 4 ) 3 H(SO 4 ) 2 [11] and Rb 3 H(SO 4 ) 2 [10]. Around the phase-transition region in phase II, the T 1 value decreases with increase in temperature.…”

“…In all the phases, very fast isotropic reorientation of NH 4 + ions takes place. The reorientation rate is about 200 MHz at 150 K in (NH 4 ) 3 H(SO 4 ) 2 [11]. In phase II, the acidic protons undergo a very fast local and anisotropic motion, probably a wobbling motion of the O-H bond in one direction.…”

“…In the previous works, dynamic behavior in [(NH 4 ) 1 − x Rb x ] 3 H (SO 4 ) 2 (0 b x b 1) was studied extensively [22] as well as those in (NH 4 ) 3 H(SO 4 ) 2 [11] and Rb 3 H(SO 4 ) 2 [10]. In all the phases, very fast isotropic reorientation of NH 4 + ions takes place.…”

“…In those compounds, tetrahedral XO 4 anions form hydrogen bond networks. Previously, we studied proton dynamics in CsHSO 4 [7][8][9], Rb 3 H(SO 4 ) 2 [10], (NH 4 ) 3 H(SO 4 ) 2 [11] and so on by means of 1 H solidstate NMR, which is suitable to study dynamics at atomic levels. We concluded that a motion breaking the hydrogen bonds is ratedetermining in the proton diffusion.…”

Discussion of unusual hydrogen atom display in solid acids

“…The size of this volume is at least in the range of the X-ray coherence length ($1 mm). The reorientations of the HAO 4 groups occur relatively rarely, if they are examined in the time scale of X-ray scattering [10][11][12], i.e. the residence time of the orientation states is much larger than the characteristic time of the X-ray scattering process.…”