Adsorption-induced distortion of F16CuPc on Cu(111) and Ag(111): an X-ray standing wave

The adsorption geometry of perfluorinated copper-phthalocyanine molecules $({\mathrm{F}}_{16}\mathrm{CuPc})$ on Cu(111) and Ag(111) is studied using x-ray standing waves. A detailed, element-specific analysis taking into account nondipolar corrections to the photoelectron yield shows that on both surfaces the molecules adsorb in a lying down, but significantly distorted configuration. While on copper (silver) the central carbon rings reside 2.61 \AA{} (3.25 \AA{}) above the substrate, the outer fluorine atoms are located 0.27 \AA{} (0.20 \AA{}) further away from the surface. This nonplanar adsorption structure is discussed in terms of the outer carbon atoms in ${\mathrm{F}}_{16}\mathrm{CuPc}$ undergoing a partial rehybridization $(s{p}^{2}\ensuremath{\rightarrow}s{p}^{3}).$