Compressibility and Vibrational Modes in Solid As4O6

The phonon spectrum of solid As4O6(arsenolite,Fd3m,Z=8) ambient and high pressures is studied with Raman and infrared spectroscopies and analyzed in relation to the vibrational spectrum of the adamantane As4O6molecule in the vapor state. The behavior of arsenolite upon compression can be interpreted as a result of an enhancement of intermolecular interactions between two equivalent As4O6molecules at Tdsymmetry sites of the "primitive" unit cell. The enforced interactions between the molecules through intermolecular O···O repulsions lead to a large increase of correlation field splittings of the internal vibrations due to the predominant bending and bridge stretching deformations. Eventually, at about 6 GPa they lift degeneracies of the internal modes and lower the symmetry of the crystal lattice. The observed phase transition in solid As4O6is reversible without any hysteresis.