Richard Buchner, Christian Hölzl, Jochen Stauber and Josef Barthel
Complex permittivity spectra of aqueous solutions of Me4NBr, Et4NCl, Et4NBr, Pr4NBr, Bu4NBr, and Pe4NBr were determined in the frequency range 0.2 ≤ υ/GHz ≤ 89. At 25 °C data cover electrolyte concentrations up to the saturation limit. Additionally, selected concentrations of Pr4NBr and Bu4NBr were investigated as a function of temperature. The spectra of Me4NBr, Et4NCl, and Et4NBr exhibit three dispersion steps which can be assigned –with falling relaxation time –to the tumbling motion of ion-pairs, the co-operative relaxation of the H-bond network of ´bulk´ water and the fast reorientation of mobile H2O molecules. For Pr4NBr, Bu4NBr, and Pe4NBr an additional dispersion step emerges, which is assigned to H2O in the hydration shell of the tetraalkylammonium ions. Compared to ´bulk´ water the dynamics of this ´slow´ water is reduced by a factor of 2.5 - 3 and the average number of hydrogen binds is increased from n-HB = 2.5 to n-HB = 3.5.