Vibrational spectroscopy at very high pressures. Part 18.—Three solid phases of benzene

Abstract

Using a diamond anvil cell (d.a.c.) the high pressure phase II of solid benzene has been characterised by Raman, mid-i.r. and far-i.r. spectroscopy on the same sample. The three i.r.-active lattice modes observed at 20.4 kbar (108, 121, and 157 cm^–1) are close to those predicted by Ellenson and Nicol on the basis of an atom–atom potential function. Compression of benzene to ∼40 kbar followed by heating at 100°C induced a sluggish transition to benzene III characterised by large increases in lattice mode frequencies, but not in the numbers of bands. The status of benzene III is discussed.