| Popis: |
Raman spectra are presented for pure solid and liquid $sup 3$He, $sup 4$He, and $sup 4$He/subx/ $sup 3$He$sub 1$/sub -//subx/ solutions for frequency shifts from 10 to 300 K. The data for all phases show a broad peak. In the solids this peak corresponds reasonably well with the scattering expected from the phonons near the zone boundary. In the liquids a similar interpretation is possible although not compelling. The data from all phases also show a large amount of intensity beyond that corresponding to the maximum of twice a phonon frequency which has a monotonically decreasing dependence on frequency shift. The high-frequency tail extends out to 300 K in the higher density solids (17 cm$sup 3$/mole). This feature of the spectra, which is absent in classical solids, is found to correspond to a Raman process where a photon Raman scatters, producing a pair of energetic nearly-free particles with equal and opposite wave vector. The details of this model are explored both theoretically and experimentally. (AIP) |
