- AMER CHEMICAL SOC
Cationic rhodium clusters, Rh-n(+) (n = 4-8), were prepared in the gas phase by the laser ablation of a Rh rod. The Rh-n(+) clusters were introduced into a reaction gas cell filled with nitric oxide (NO) diluted with He, where they were subjected to collisions with NO and He in a thermal equilibrium at 300 K. The NO molecules were found to adsorb sequentially on the Rh-n(+) clusters forming Rh-n(+)(NO)(m). To examine the adsorption form and the reaction of NO, we heated Rh-n(+)(NO)(m) in an extension tube located after the reaction gas cell and the thermal response of the clusters, desorption of the fragments, was recorded as a function of temperature (300-1000 K). The desorption of NO molecules was predominantly observed below 500 K, giving either Rh-n(+)(NO)(n+1) or Rh-n(+)(NO)(n+2), which indicates that there were NO molecules loosely adsorbed on the Rh-n(+) clusters. Further desorption was found to proceed at higher temperatures (500-1000 K), whereby NO was released from the smaller clusters, Rh-n(+) (n <= 5). In contrast, for the larger clusters (n >= 6), N-2 release was clearly observed at high temperatures (>800 K). Thus, the reduction of NO occurred for larger clusters at higher temperatures.
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