Spatial structure determination of (√3×√3)<i>R</i>30° and (1.5×1.5)<i>R</i>18° CO or Cu(111) using angle-resolved photoemission extended fine structure

Abstract

We report a study of the spatial structure of ($\sqrt{3}$\ifmmode\times\else\texttimes\fi{}$\sqrt{3}$)R30\ifmmode^\circ\else\textdegree\fi{} and (1.5\ifmmode\times\else\texttimes\fi{}1.5)R18\ifmmode^\circ\else\textdegree\fi{} 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) \AA{} in the ($\sqrt{3}$\ifmmode\times\else\texttimes\fi{}$\sqrt{3}$)R30\ifmmode^\circ\else\textdegree\fi{} phase and 1.91(2) \AA{} in the (1.5\ifmmode\times\else\texttimes\fi{}1.5)R18\ifmmode^\circ\else\textdegree\fi{} phase. The first layer Cu-Cu spacing is 2.07(3) \AA{} in the ($\sqrt{3}$\ifmmode\times\else\texttimes\fi{}$\sqrt{3}$)R30\ifmmode^\circ\else\textdegree\fi{} phase. The first layer Cu-Cu spacing in the (1.5\ifmmode\times\else\texttimes\fi{}1.5)R18\ifmmode^\circ\else\textdegree\fi{} phase is 2.01(4) \AA{}, a contraction of 3% from the clean metal value of 2.07 \AA{}. We calculate the bending mode force constant (1.5\ifmmode\times\else\texttimes\fi{}1.5)R18\ifmmode^\circ\else\textdegree\fi{} phase to be ${\mathit{k}}_{\mathrm{\ensuremath{\delta}}}$=2.2(1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$ dyn/cm rad from the above bond lengths combined with previously published infrared absorption frequencies. \textcopyright{} 1996 The American Physical Society.