A low-energy electron diffraction intensity analysis of Cu(001)c(2×2)-Cl

A LEED intensity analysis of the Cu(001)c(2*2)-Cl structure finds the Cl atoms in the fourfold symmetrical hollow sites with a Cl-Cu interlayer spacing of 1.60+or-0.03 AA and a slightly expanded Cu-Cu first interlayer spacing of 1.85+or-0.03 AA (bulk value 1.807 AA). The calculated Cu-Cl bond length is 2.41+or-0.02 AA, in fair agreement with the value 2.37+or-0.02 AA determined with SEXAFS by Citrin and co-workers (1978, 1982). The effect of the Cl scattering potential on the LEED intensities, and hence on the structural parameters, is quantitatively analysed with r-factor calculations. The results obtained in this work speak in favour of the same overlayer model found by an earlier LEED analysis of the closely related Ag(001)c(2*2)-Cl structure but contradicted by photoemission studies, and thus help resolve the discrepancy between LEED and photoemission about the atomic geometry of this system in favour of the LEED structure.