Vibrational spectroscopy at high pressures. Part 37.—Infrared spectrum of anthracene

Abstract

Mid-i.r. spectra have been obtained for anthracene at hydrostatic pressures up to 45 kbar. Plots of mode frequency against pressure indicate the existence of a second-order phase transition at 24 ± 2 kbar, previously detected only under conditions of high shear stress. The Landau criterion and the spectroscopic evidence show the new phase to be triclinic, P1 with z= 2. It is identified with a metastable phase recently obtained by Thomas and coworkers using different types of stress.