The infrared spectrum of CO chemisorbed on aluminahyphen;supported Rh atoms has been investigated. In agreement with previous work, three types of adsorbed species have been clearly distinguished on the basis of their Cndash;O stretching frequencies. Species I, assigned as Rh(CO)2, is formed only with Rh atoms which are isolated from each other. Species II, assigned as Rhndash;CO, and III, assigned as Rh2CO, are formed on Rh clusters having two or more Rh atoms. COhyphen;species II and III undergo interactions with neighbor CO species causing an increase in wave number as coverage increases. Based on infrared intensity measurements for species I, the OCndash;Rhndash;CO angle is sim;90deg;. Chemisorbed13CO yields the expected infrared spectrum on Rh, and rapid isotopic exchange between13CO(ads) and12CO(g) is observed which cannot be explained by the observed rate of desorption of CO from the supported Rh surface.
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