Determination of Adsorbate Geometries from Intramolecular Scattering in Deep-Core-Level X-Ray Photoemission: CO on Ni(001)

Abstract

In angle-resolved x-ray photoemission from the C $1s$ level of CO adsorbed on Ni(001), a peak in intensity with magnitude $\frac{{I}_{max}}{{I}_{\mathrm{back}}}\ensuremath{\approx}1.5$ and full width at half maximum \ensuremath{\approx} 25\ifmmode^\circ\else\textdegree\fi{} is found to point along the surface normal. Single-scattering calculations for both a single CO molecule and a finite cluster verify that this peak is due to intramolecular scattering by O. The average orientation of CO is thus determined to be within 12\ifmmode^\circ\else\textdegree\fi{} of normal, with an undetermined rms vibrational notion of \ensuremath{\lesssim} 35\ifmmode^\circ\else\textdegree\fi{}.