The molecular vibrations of the B12H-12 molecule are studied in the first part. At the beginning, the symmetry properties of the icosahedral modes are discussed. Then, the Raman and i.r. data for B12H-12 are analyzed using various valence force field model potentials. With a six-parameter model we obtain a mean deviation of ~2 per cent for the nine measured frequencies. We find strong and angular-dependent forces pointing outward from the icosahedron; however, the intra-icosahedral forces are relatively weak and much less angle-dependent. We also investigate the -q = 0 phonons of elemental boron crystals. For α-rhombohedral boron, we obtain good agreement with the measured Raman lines; we also are able to reproduce the main features of the one-phonon density of states of β-rhombohedral boron. We find that the coupling constants of the strong inter-icosahedral bonds are 2̃5% larger than the intra-icosahedral ones. The latter change very little as compared to B12H-12. Altogether our results support the idea that within the icosahedron, the binding is metal-like, whereas the outward bonds are more covalent.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Physics and Chemistry of Solids|
|State||Published - Sep 1975|
ASJC Scopus subject areas
- Materials Science(all)
- Condensed Matter Physics