Muon spin resonance (? SR) and deuteron nuclear magnetic resonance (²H NMR) were used to investigate the cation dynamics in pyridinium tetrafluoroborate ([C? H? NH]?[BF?]?). Compared to the macroscopic data the results show the individual ionic contribution permitting the interpretation of the intermolecular interaction which leads to ferroelectricity. Additional ? SR measurements were performed on pyridinium perchlorate ([C? H? NH]?[ClO?]?) as the perchlorate shows a ferroelectric solid-solid phase transition of first order. This is in contrast to the tetrafluoroborate which shows a second order transition. The selectivity and efficiency of catalytic reactions in zeolites are mostly determined by the dynamics of the guest molecules because the latter is not only responsible for the mobility of the guest molecules within the lattice itself but also for the translational mobility to the active centers. In faujasites of type NaX and NaY the sodium ions were partly exchanged by metal ions (Pt²?, Pd²?, Ag?, Ni²?, Zn²?, Mn²?) in an aequous ion exchange procedure, and the zeolite was loaded with benzene. Compared to the ? SR spectra of pure benzene the spectra of the metal exchanged zeolites show shifts of the resonance positions.
