The alignment of a surface species determined by FT-RAIRS: Rhodium gem-dicarbonyl on TiO2(110)

p-polarised and s-polarised FT-RAIRS measurements have been carried out as a function of azimuthal angle Phi of the incident radiation on the rhodium gem-dicarbonyl species Rh(CO)(2) adsorbed on TiO2(110). The intensity of nu(sym)(C-O) in the p-polarised spectra is independent of Phi. The intensity of nu(asym)(C-O), however, exhibits a dependence on Phi in both the s-polarised and p-polarised spectra. When coupled to the tangential component of the p-polarised field, nu(asym)(C-O) exhibits a absorption band with maximum intensity at Phi=90 degrees, corresponding to alignment of the field in the [110] azimuth. The s-polarised field must be polarised in the [110] direction for nu(asym)(C-O) to be observed as a transmission band, corresponding to an incidence angle Phi=0 degrees. The results indicate a preferential alignment of the Rh-C-O bonds along the [110] azimuth. There is evidence that a minority species of misaligned Rh(CO)(2) species is also present.