Structural studies of formate and methoxy groups on the Cu(100) surface using NEXAFS and SEXAFS

Local chemisorption geometries of formate (HCO₂) and methoxy (CH₃O) groups on Cu(100) were examined by means of surface extended (SEXAFS) and near-edge X-ray absorption fine structure (NEXAFS) measurements above the O K edge. At 300 K the oxygen of the formate group are equivalent and asymmetrically located near the four-fold hollow site yielding two CuO distances between 2.31 and 2.45 Å. These distances are at least 0.3 Å longer than typical CuO distances of surface and bulk compounds due to a Cu-C steric interaction. The CO bonds and the OCO angle of the formate are estimated to be $\text{1.27 ± 0.04}\text{A}\text{?}$ and 127 ± 7°, respectively. At 200 K the methoxy group has a CuO distance of $\text{1.97 ± 0.05}\text{A}\text{?}$ and the CO axis is tilted with respect to the surface normal. The exact chemisorption site of the methoxy goup could not be determined, but the atop site is ruled-out.