Adsorption and geometry of the chemisorbed benzoate species on Cu(1 1 0)

The adsorption of benzoic acid onto the Cu(1 1 0) surface has been studied by temperature programmed desorption (TPD) and by the time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD) technique. Condensed multilayers of undissociated benzoic acid form at high benzoic acid exposures at 81 K surface temperature, and desorption of the multilayer has been observed at 270 K. Adsorbed benzoic acid in the first layer decomposes to chemisorbed benzoate upon heating. The H+ ion emission pattern observed upon electron stimulated desorption indicates that the benzoate species is bound by its carboxylate moiety to two close-packed Cu atoms, with the molecular plane parallel to the 〈 1 1 ¯ 0 〉 crystal azimuth. Three prominent H+ beams are emitted from the 3-, 4-, and 5-positions on the phenyl ring, and these beam orientations indicate that the axis of the benzoate molecule is normal to the crystal face. The angle analysis shows that the initial angle of H+ ion emission from the 3- and 5-positions in the phenyl ring is 64° with respect to the surface normal.