No abstract

No abstract

The nature of the broad band of microscopic excitations measured in molten gallium is investigated by means of analysis of their mode eigenvectors I͑Q , ͒. The results, derived from neutron spectroscopy experiments, show that excitations with a dominant acoustic character are confined to low energy transfers. In contrast, those appearing at higher frequencies unmistakably exhibit optical character, as evidenced by the out-of-phase relationship shown by the phase of oscillations in I͑Q , ͒ that become significantly shifted relative to those of the static structure factor. Such effects are shown to arise from partial covalency that is already known to be present in gaseous, cluster and crystalline forms.

The thermal conductivity ͑T͒ of the crystalline and glassy phases of the two isomers of propyl alcohol has been measured. The two isomers differ by a minor chemical detail involving the position of the hydroxyl group with respect to the carbon backbone. Such a difference in molecular structure leads, however, to disparate behaviors for the temperature dependence of ͑T͒, for both glass and crystal states. The ͑T͒ for the glass shows for 1-propanol an anomalously large plateau region comprising temperatures within 6 -90 K, while data for isomeric 2-propanol show only a small plateau up to 10 K which is comparable to data on lower alcohols. The results emphasize the role played by internal molecular degrees of freedom as sources of strong resonant phonon scattering.