Vibrational spectroscopy at very high pressures. Part 16. A Raman and infrared study of mercury(II) bromide

Abstract

All the four solid phases I, II, III, and IV of HgBr₂ have been characterised by i.r. and Raman spectroscopy under hydrostatic or near-hydrostatic conditions in a diamond anvil cell. The structures of the three high-pressure phases are discussed on the basis of the spectral evidence with the conclusions: IV probably has the CdI₂ structure, or a polytype thereof; III appears to have a (probably unique) monoclinic molecular structure with factor group C_2h; the structure of II is closely related to I but cannot be deduced from present evidence. The natures of the transitions I–IV in HgCl₂ and I–II in HgBr₂ are contrasted.