High-pressure structural properties of naphthalene up to 6 GPa

Abstract

The elastic and structure behavior of solid naphthalene (C10H8) was studied byin situsynchrotron powder X-ray diffraction up to 5.6 GPa in a diamond anvil cell. Rietveld refinements were applied to obtain atomic coordinates and lattice parameters as a function of pressure. Within the studied pressure range, the intramolecular C—C and C—H distances decrease by 3.5%, whereas intermolecular distances within and between the herringbone layers decrease by 18 and 10%, respectively. Noindication of a symmetry change (space groupP21/a) was observed. A markedly anisotropic compression is preserved up to 5.6 GPa, with linear compressibilities βa:βb:βc:β[200]≃ 7:5:3:10. Fitting of theP–Vexperimental data to the Vinet equation of state yieldsK0= 7.9 (3) GPa andK′ = 7.5 (3) atV0= 361 Å3. At the highest pressure of 5.6 GPa, the unit-cell volume is decreased by 23%. The overall regularity of compression confirms the absence of major structural transformations in naphthalene up to 5.6 GPa. However, a distinct bend of the pressure dependence of the interlayer C...C distances observed at 2 GPa suggests a minor structural irregularity, which is apparently associated with spectroscopic anomalies observed previously.