Structure of Pressure-Induced Fibrous Sulfur

Abstract

The arrangement of the sulfur helices in the pressure-induced fibrous form of sulfur has been determined from three-dimensional x-ray diffractometer data. The crystals show orthorhombic diffraction symmetry, but analysis of their structure has shown that the most probable space group is P2 and that the orthorhombic symmetry results from multiple twinning. The pseudo-orthorhombic unit cell contains 16 ten-atom helix segments, half of which are right-handed and half left-handed, in an essentially close-packed arrangement. The monoclinic unit cell, which contains 8 ten-atom segments, has lattice constants a = 17.6, b = 9.25, c = 13.8 Å and β = 113°. There is strong evidence that the pressure-induced fibrous form and the ψ form have the same structure.