Gas-Phase Chemical Reactions of Transition Metal Clusters with Simple Molecules
Chemical reactions of isolated transition metal clusters are studied in a laser-vaporization cluster source coupled to a continuous-flow reactor. Detection of reaction products is via laser ionization and time-of-flight mass spectrometry. Experimental probes that have been developed include: 1) kinetics measurements, in which the disappearance of bare cluster signal with increasing reagent gas flow is used to determine absolute reaction rate constants for the addition of the first adsorbate molecule; 2) product composition measurements, in which inferences as to cluster structure and the nature of surface binding sites are derived by determining the total number of adsorbates the clusters can accommodate; 3) laser-induced desorption experiments, from which adsorbate binding energies can be derived; and 4) the observation of actual chemical reactions on cluster surfaces, such as hydrogen/ deuterium exchange or adsorbate photochemistry. In addition, a new experimental procedure has been developed that, in a single series of measurements, provides measures of the first three parameters listed above. A review is given of earlier studies of the reaction of iron clusters with hydrogen. More recent results on the reaction of iron clusters with ammonia, and the reaction of ammoniated iron clusters with hydrogen, are also presented.
KeywordsLaser Fluence Cluster Surface Iron Cluster Transition Metal Cluster Absolute Rate Constant
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- 6.The rate constants shown in Fig. 2 are somewhat different from those initially reported in Ref. 1. The principal change is in the earlier assumption that the cluster flow velocity in the FTR is equal to the average He flow velocity. In fact, as further experiments have shown, the clusters tend to stay in the middle of the FTR channel, where their velocities are roughly twice the average He velocity.Google Scholar