Calculated high-pressure properties of solid acetylene and possible polymerization paths

Abstract

Results of theoretical calculations at 0 K on the two known structures of solid acetylene using the modified Gordon–Kim plus damped dispersion model are reported. The lattice energy of the low temperature Cmca structure is compared to that of the high temperature Pa3 structure at zero pressure and found to be slightly less stable, though a very small pressure (about 0.25 kbar) stabilizes the Cmca structure relative to the Pa3 structure. Agreement between the experimental structure and energy for the Cmca structure and our present results is good. Structural properties of the Cmca structure were calculated to 100 kbar as well as the pressure dependence of the Ag libron mode. A possible high-pressure path for the polymerization of solid Cmca acetylene that would lead to a well-ordered polymer was proposed, but calculations of C–C distances suggest that a more cross-linked product would be favored.