Three distinct geometries of surface‐adsorbed carboxylate groups

The surface geometry of carboxylate groups was studied by analysis of the SERS spectra of aromatic carboxylic acids adsorbed on silver colloid surfaces. Three distinct types of carboxylate group surface geometry were identified. In the flat geometry, the CO2- group interacts with the surface through its π-electrons, and the νs(COO-) band is very strong whereas the δ(COO-) band is very weak. In the two-legged standing up geometry, the CO2- group is adsorbed through both of its oxygen atoms, but tilted with respect to the surface. The relative intensity of the δ(COO-) band with respect to the νs(COO-) band increases as the tilt of the carboxylate group to the surface increases. Finally, in the one-legged geometry, only one oxygen of the CO2- group is adsorbed on the surface and the δ(COO-) band is stronger than the νs(COO-) band. © 1998 John Wiley & Sons, Ltd.