We report a study of the spatial structure of ($\sqrt{3}$×$\sqrt{3}$)R30° and (1.5×1.5)R18° CO adsorbed on Cu (111), using the angle-resolved photoemission extended fine structure (ARPEFS) technique. The ARPEFS data were taken along the surface normal-emission direction with a sample temperature of 80 K. The CO molecule adsorbs on an atop site for both adsorption phases. Full multiple-scattering spherical-wave (MSSW) calculations were used to extract the C-Cu bond length and the first Cu-Cu layer spacing for each adsorption phase. The C-Cu bond length is 1.91(1) Å in the ($\sqrt{3}$×$\sqrt{3}$)R30° phase and 1.91(2) Å in the (1.5×1.5)R18° phase. The first layer Cu-Cu spacing is 2.07(3) Å in the ($\sqrt{3}$×$\sqrt{3}$)R30° phase. The first layer Cu-Cu spacing in the (1.5×1.5)R18° phase is 2.01(4) Å, a contraction of 3% from the clean metal value of 2.07 Å. We calculate the bending mode force constant (1.5×1.5)R18° phase to be ${\mathit{k}}_{\mathrm{\delta }}$=2.2(1)×${10}^{\mathrm{-}12}$ dyn/cm rad from the above bond lengths combined with previously published infrared absorption frequencies. © 1996 The American Physical Society.

• Received 19 June 1996

DOI:https://doi.org/10.1103/PhysRevB.54.10862