Identification of Mono- and Bidentate Carboxylate Surface Species on Cu(111) using X-Ray Absorption Spectroscopy

Abstract
In order to identify the nature of the bond which is formed when anhydride containing molecules such as pyromellitic dianhydride (PMDA) react with a Cu surface we have carried out measurements using x-ray absorption spectroscopy (NEXAFS) at the Cls and Ols edges. By comparing to reference spectra for benzoic acid bound to Cu surfaces the position of the resonances in NEXAFS-spectra for monolayers of PMDA on a Cu(111)-substrate can be shown to be fully consistent with the presence of a bidentate surface species. Evidence is provided that monodentate species show a characteristic shift of the Cls-π_CO-excitation to 287.6 eV (from 288.05 eV for the bidentate species).