Adsorption of nitrobenzene and some simple derivatives on the Cu{110} surface

The chemistry of nitro- and amine-substituted aromatic molecules on a Cu(110) surface has been studied using Fourier transform infrared spectroscopy, by comparison of the adsorption of nitrobenzene (NB), p-dinitrobenzene (pDNB) and p-nitroaniline (pNA). When nitrobenzene was adsorbed on a clean Cu(110) surface at room temperature, it decomposed to form a phenyl species with the C-2 axis nearer the surface normal than parallel. At 83 K, multilayer nitrobenzene formed with a vibrational spectrum, in good agreement with gas-phase data; upon warming, a phenyl species remained, which was stable to about 350 K. AES of the species present following dosing at 300 K showed carbon and oxygen but no nitrogen. When p-dinitrobenzene was adsorbed it decomposed, losing one NO2, to form a stable nitrophenyl species on Cu(110) orientated with the C, axis closer to the surface normal than the phenyl species derived from nitrobenzene. In contrast, p-nitroaniline does not decompose on the Cu(110) surface at room temperature. Multilayer and monolayer p-nitroaniline are distinguished by frequency shifts of NO2 and NH2 modes, attributed to intermolecular hydrogen bonding. In the monolayer, the amine group appears to stabilise the ring-nitro group bond, allowing bonding to the surface via the NO2 group in an orientation perpendicular to the surface.