High resolution neutron powder diffraction studies of the low temperature crystal structure of molecular iodine (I₂)

The crystal structure of iodine has been investigated using high resolution neutron time-of-flight powder diffraction in the temperature range 5 to 150 K. The results confirm the structure is orthorhombic, space group Cmca, and is isomorphous with the solid halogens bromine and chlorine. The accurate structural parameters obtained in this investigation have been modelled assuming a simple Einstein functionality to compare the refined anisotropic temperature factors with the directly determined molecular dynamics and predict minimum energy (0 K) lattice parameter values. These values are expected to be directly applicable in the development and verification of anisotropic atom-atom pair potentials which will successfully reproduce the observed condensed phase crystalline structure.