| Autor: |
Torchet, G., de Feraudy, M.-F., Raoult, B., Farges, J., Fuchs, A. H., Pawley, G. S. |
| Předmět: |
|
| Zdroj: |
Journal of Chemical Physics; 6/1/1990, Vol. 92 Issue 11, p6768, 7p |
| Abstrakt: |
Clusters made of several hundreds of SF6 molecules are produced in the free jet expansion of a Ne–SF6 mixture and studied by electron diffraction methods. Cold clusters have the monoclinic structure which has been identified recently in a polycrystalline sample at and below 85 K. Clusters adopt the body centered cubic structure of the bulk plastic phase when they are warmed up after crossing the frontal shock wave. Diffraction patterns show a progressive evolution, particularly in several line heights, from the low to the high temperature structure. In order to account for these intermediate states, a 512-molecule cluster is simulated by molecular dynamics on the DAP computer, using a rigid-molecule model with a single Lennard-Jones atom–atom potential. Warming up the model from 50 to 160 K by steps of 5 K, it is found that the structural transition occurs between 90 and 120 K. Calculated diffraction functions are in very good agreement with experimental patterns for both crystalline structures and for the intermediate stages. Intermediate experimental patterns can thus be attributed to the evolution of single clusters rather than to the coexistence of clusters with different structures. According to the model, the high temperature structure is initiated by surface molecules, which suggests that a surface effect is responsible for the temperature spread of the transition. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
|
