X-ray structural study of trans-polyacetylene at high pressure

Abstract The evolution with hydrostatic pressure (0 trans -polyacetylene was measured using 4-circle synchrotron x-ray diffractometry and a Merrill-Bassett diamond anvil cell. The P-dependence of (HK0) reflections signify a lowering of the two-dimensional space group symmetry from pgg to p2 with a threshold P a and b axes of about 92° throughout the entire P range. The interchain compressibility is large and highly anisotropic. Below 6 kbar, Δa/a and Δb/b are 8.3 × 10 −3 /kbar and 3.8 × 10 −3 /kbar respectively. Both a and b stiffen above 6 kbar as the system approaches true close-packing.