Modelling X-ray scattering factors from fluids of some fluorinated molecules and related compounds

There is current interest, both for basic science and technological applications, in fluorocarbons such as CF 4 and the related molecules. Here we first report a Hartree-Fock calculation of the ground-state electron density in the octahedral molecule SF 6 using the experimentally determined bond length. From this density, the number of electrons lying inside a sphere of radius r, denoted by Q(r), centred on the S nucleus has been extracted. The X-ray scattering factor f(k) is then modelled using Q(r) and compared with f(k) for the isoelectronic united atom ytterbium. The molecule CF 4, together with its isoelectronic partners PF 3, CrF 2 and AsF, is again compared with regard to f(k) with the united atom Mo. Finally, interest in modelling PbF is pointed out, in relation to the quantum-chemical theory already available