Recent experimental studies of liquids have shown that phonon- like collective excitations seem to exist in some liquids but not in others. Consequently the assumption for the ideal phonon theory used to describe lattice dynamics is analysed, and non-crystalline materials are classified according to which assumptions are obeyed and which are violated. The neutron scattering results from liquid H2 are critically analysed with the result that the concept of phonons must be introduced to understand this liquid, and consequently the phonons are quantitatively discussed. In liquid N2 no evidence of phonons is seen in the neutron scattering pattern, in agreement with the results obtained for liquid A. The influence of the rotational degrees of freedom in liquid N2 is briefly discussed. The results presented together with similar results obtained from the liquids A, He, and Rb support the classification mentioned above, and indicate how further understanding of the dynamics of liquids may be gained. In an appendix the use of a neutron triple axis crystal spectrometer in the study of liquids is discussed.
|Place of Publication||Roskilde, Denmark|
|Publisher||Risø National Laboratory|
|Number of pages||54|
|Publication status||Published - 1974|
|Series||Denmark. Forskningscenter Risoe. Risoe-R|
- Risø report 308