Orientational ordering of commensurate Fe(CO)5monolayers on graphite

Elastic neutron diffraction and Mössbauer spectroscopy have been used to study the structure, orientational-disordering (OD) transition, and melting of an Fe${\mathrm{}\left(\mathrm{CO}\right)\mathrm{}}_5$ submonolayer adsorbed on Grafoil. The OD transition occurs between 150 and 167 K from a two-sublattice ($\sqrt{7}\times \sqrt{21}$) structure to a nearly ($\sqrt{7}\times \sqrt{7}$) phase in which the molecules are believed to rotate about the surface normal. Mössbauer spectra exhibit a more abrupt variation with temperature near melting at 170 K than through the OD transition.