Proton dynamics in phase II of CsHSO4 as probed by 1H spin–lattice relaxation

Proton dynamics in phase II of CsHSO4 have been studied by means of 1H spin–lattice relaxation. The mechanism of the 1H spin–lattice relaxation in phase II has been discussed from temperature and field dependences of the relaxation time. Chemical shift anisotropy is suggested to contribute to the relaxation in addition to dipole–dipole interactions between 1H spins and between 1H and 133Cs spins. Motions faster than the SO4 reorientation are proposed for phase II; a proton transfer between two SO4 tetrahedra along a hydrogen bond and a local motion of Cs+ ions, and their mean residence times are estimated. The 1H chemical shifts determined from MAS NMR spectra demonstrate that the hydrogen-bond strength is stronger in phases III than in phase II. This leads to the rigid nature of phase III compared with phase II.