The crystal structure of methane phase III

Methane is the simplest organic molecule, and like many supposedly simple molecular materials it has a rich phase diagram. While crystal structures could be determined for two of the solid phases, that of the low temperature phase III remained unsolved. Using high-resolution neutron powder diffraction and a direct-space Monte Carlo simulated annealing approach, this fundamental structure has now finally been solved. It is orthorhombic with space group Cmca , and 16 molecules in the unit cell. The structure is closely related to that of phase II, yet is no subgroup of it. © 2003 American Institute of Physics. @DOI: 10.1063/1.1580809#