Nitrobenzene adsorption on clean and NaCl-covered Cu(100), Ni/Cu(100), Ag/Cu(100) and Na/Cu(100) surfaces studied by XPS and XAES

Abstract

Adsorption of nitrobenzene on clean and NaCl-covered Cu(100), Ni/Cu(100), Ag/Cu(100) and Na/Cu(100) surfaces has been studied by X-ray photoelectron spectroscopy and X-ray-induced Auger electron spectroscopy. Dissociative adsorption of nitrobenzene into nitrosobenzene and phenylnitrene occurs at a lower temperature on a 1.5 monolayer (ML) Ni/Cu(100) surface than on a Cu(100) surface, and the dissociation is significantly attenuated by a 2.0 ML Ag overlayer. A portion of NaCl deposited on Cu(100), Ni/Cu(100) and Ag/Cu(100) gives disrupted or loosely bound NaCl. The metallic character of the Na of the NaCl is indicated by the formation of the nitrobenzene anion after exposure of the NaCl- and Na-covered surfaces to nitrobenzene at 176 K and 110 K, respectively. The Auger parameter (2066.2 eV) for Na atoms (0.5 ML) on Cu(100) (near the value of metallic Na) changed to 2062.7 eV (Near the value of NaNO 2) after the formation of the anion. This shows a localization of a large positive charge on Na after nitrobenzene adsorption. A mechanism for the occurrence of the metallic character of the Na from NaCl is discussed.