Vibrational spectra of carbon monoxide chemisorbed on alumina-supported nickel particles: A tunneling spectroscopy study

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Abstract
Tunnelingspectroscopy is used to study the chemisorption of CO on small nickel particles. The particles are grown from vapor on a thermally oxidizedaluminum substrate. Carbon monoxide is observed to chemisorb in at least four distinct ways, giving CO stretching frequencies of 256.5, 246, 222, and 207 meV. The 256.5 meV species has low frequency modes at 45.5 and 59.5 meV. The low frequency modes of the remaining three species are not resolved sufficiently for identification. The frequencies of all modes were found to have some coverage dependence. The largest shift is seen in a CO stretching vibration that moves from 200 to 207 meV with increasing coverage. The effect of hydrogen coadsorption is examined and evidence for the presence of oxygen on the particles is presented. The reaction of hydrogen with the CO chemisorbed on these nickel particles is found to produce very little surface hydrocarbon in contrast to results found previously for rhodium particles under similar conditions.