The adsorption of carbon monoxide on the (100) and (111) surfaces was studied experimentally using the techniques of reflection absorption infrared spectroscopy and X-ray photo-electron spectroscopy. The interaction of CO with the two surfaces was also studied with density functional theory. Both surfaces adsorbed CO molecularly at low temperatures but in markedly different forms. On the (111) surface, CO initially adsorbed at 90K in a form that yielded a CO stretching mode at 1502-1512/cm. With gentle annealing to 120K, the CO switched to a bonding environment characterized by multiple CO stretch values from 1980 to 2080/cm, assigned to one, two or three CO molecules terminally bonded to the B atoms of a triangular B3 unit at the (111) surface. In contrast, on the (100) surface only a single CO stretch was observed at 2094/cm, which was assigned to an atop CO molecule bonded to a La atom. The maximum intensity of the CO stretch vibration on the (100) surface was higher than on the (111) surface by a factor of 5. This difference was related to the different orientationsof the CO molecules on the two surfaces and to reduced screening of the CO

dynamic dipole moment on the (100) surface, where the bonding occurs further from the surface plane. On (100), XPS measurements indicated that CO dissociated on the surface at above 400K.

Probing the Properties of the (111) and (100) Surfaces of LaB6 through Infrared Spectroscopy of Adsorbed CO. Yorisaki, T., Tillekaratne, A., Ge, Q., Oshima, C., Otani, S., Trenary, M.: Surface Science, 2009, 603[19], 3011-20

Table 1

Binding Energies of Peaks in (100) XP Spectra