THE ADSORPTION OF CO ON RH(100) - REFLECTION-ABSORPTION INFRARED-SPECTROSCOPY, LOW-ENERGY-ELECTRON DIFFRACTION, AND THERMAL-DESORPTION SPECTROSCOPY

The adsorption of CO on Rh(100) has been investigated as a function of temperature and CO pressure, with reflection absorption infrared spectroscopy (RAIRS), low energy electron diffraction (LEED), and thermal desorption spectroscopy (TDS). At low coverages, most CO adsorbs linearly, up to 0.5 monolayers (ML), where a c(2×2) LEED pattern is observed. The saturation coverage at 300 K is 0.75 ML, associated with a p(4√2×√2) R45° LEED pattern, and adsorption of CO in at least three states, namely two linear modes and one bridged mode. At temperatures well below 300 K and relatively high exposures, CO is compressed into a dense hexagonal overlayer structure with a c(6×2) LEED pattern and a saturation coverage of 0.83 ML, in which the majority of the CO is bonded linearly. The activation energy of desorption for CO from Rh(100) in the limit of zero coverage is 131±4 kJ/mol and the preexponential factor is (4±3)× 1016 s-1. We compare our results with the literature of CO on Rh(100), which shows contradictory results on the vibrational spectra, LEED structures, and saturation coverages of CO. © 1994 American Institute of Physics.