Raman Spectra of Rhombohedral and α-Monoclinic Selenium under High Hydrostatic Pressure

The Raman spectra of rhombohedral, α-monoclinic, and trigonal selenium have been measured under high hydrostatic pressures up to about 8 kbar at room temperature. The frequencies of the A1-type stretching modes in both rhombohedral and α-monoclinic selenium have been observed to decrease with increasing pressure, as has that of trigonal selenium. This indicates that interference between inter- and intramolecular bondings also exists in crystals composed of ring molecules such as Se6 or Se8.