This thesis is an exhaustive work on the structural properties and vibrations of the ammonium ion in cubic perovskites and the water molecule in transition metal hydrates. Symmetry and frequencies of vibrational modes have been determined at different phases including volume hydrogen bridge effects and Fermi resonance. Raman spectroscopy has been used in conjunction with hydrostatic pressure techniques in a diamond cell and optical absorption. As a result, numerical values of some fundamental parameters related to the internal dynamics of these molecular groups, which were unknown to date, are given.
PhD thesis advisor: Prof. José Manuel Calleja. The work was done in collaboration with J. Bartolomé, E. Palacios and F. Palacio at the University of Zaragoza, J. Tornero and F. Jaque at the Autonomous University of Madrid, M. Martini and G. Spinolo at the University of Milan, and K. Stroessner, K. Syassen and M. Cardona at the Max-Planck Institute for Solid State Research.