Infrared spectroscopic investigation of the rhodium gem-dicarbonyl surface species

The infrared spectrum of the Al2O3—supported surface species RhI(CO)2 has been measured for systematic isotopic substitution of CO18 for CO16. Six infrared bands are observed for the three possible isotopic species, confirming that the species is RhI(CO)2(C2v). Force constants for the C–O stretching motion and for CO–CO interaction between the two CO ligands on RhI(CO)2 have been evaluated, and used to predict the spectrum of RhI(CO16) (CO18) which is in good accord with the experimental observations. Agreement of these force constants with the work of Knozinger et al. on various anchored RhI(CO)2 complexes provide further confirmation of the spectral assignment. Kinetic and infrared intensity measurements of the exchange process at 200 K indicate that the exchange occurs under nonequilibrium conditions, caused most likely by the participation of a slow CO diffusion process which is rate controlling.