A VIBRATIONAL STUDY OF CHEMISORBED 3-THIOPHENE CARBOXYLATE ON CU(110)

The chemisorption of 3-thiophene carboxylate (C4H3SCO2-) on Cu(110) fo llowing room temperature exposure of the metal to the parent carboxyli c acid has been investigated by ultra-high resolution electron energy loss spectroscopy. By taking advantage of improvements in spectrometer design and the application of maximum entropy based, data analysis te chniques, it has been possible to determine almost all of the vibratio nal frequencies associated with this chemisorbed species. Spectra were measured at a resolution of 23 cm(-1) and a further improvement by ab out a factor 2 was obtained by subsequent data processing. As anticapt ed, the molecule adopts an upright orientation at saturation coverage and modes with their dipole moment change polarised predominantly para llel to the ring-CO2 bond are the most intense in specular scattering. Modes of C-H bending character are strongly enhanced in off-specular scattering. A strong, dipole active mode at 297cm(-1) is tentatively a ssigned to a collective mode of the close-packed molecules based on th e out-of-plane bending of the aromatic ring relative to the carboxylat e plane.