A new interpretation is presented of the vibrational band shapes of the pro
ton disordered ice Ih and Ic in the OH and OD stretch region. The vibration
ally excited states are shown to be related to those of a periodic system,
whose unit cell is composed of four oscillating dipoles in a tetrahedral ar
rangement around an O-atom. Analysis of the excitations in this periodic sy
stem and of the perturbation induced by disorder is used to provide a detai
led assignment of the band shapes of the measured spectra. (C) 1999 America
n Institute of Physics. [0021-9606(99)00707-2].