ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
The reactions of neutral iron clusters Fe7–27 with water are studied in a laser-vaporization cluster source coupled to a continuous-flow reactor. Reaction products are detected via laser ionization and time-of-flight mass spectrometry. The reactions of room-temperature clusters with H2O show adsorbate decomposition and hydrogen desorption, as do the reactions with D2O at elevated temperatures. The room-temperature reaction with D2O appears not to involve any decomposition, and is at equilibrium under the conditions of these experiments. The dependence of reaction extent on D2O pressure yields equilibrium constants for the addition of the first and second D2O molecules. The analysis is complicated by the presence of two-photon ionization processes that are treated quantitatively with a rate-equation model. This treatment also yields estimates for cluster photoabsorption cross sections, which are found to be approximately linear in cluster size, having a magnitude of 2.3×10−17 cm2 per iron atom. From the derived equilibrium constants and estimated adsorption entropies, approximate D2O–cluster binding energies are determined. They range from 0.42 to 0.59 eV, and their dependence on cluster size shows a remarkable similarity to the dependence of the rate constants for reaction of iron clusters with H2. The implications of this similarity are discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.456760
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