Measurements of second moment of H-1 NMR line, spin-lattice relaxation
time and complex permittivity have been performed for polycrystalline
pyridinium iodide as a function of hydrostatic pressure and temperatu
re. The influence of pressure on molecular reorientation of the pyridi
nium cation was analysed. The occurrence of reorientations between the
potential energy minima of different depths in the low-temperature ph
ase was confirmed. With increasing pressure the height of the E-B barr
ier was found to increase while that of the E-C barrier and asymmetry
parameter Delta was found to decrease.