title: Theoretical Investigation of the Reaction Paths of the Aluminum Cluster Cation with Water Molecule in the Gas Phase: A Facile Route for Dihydrogen Release.
abstract: The gas-phase reaction of the Al6(+) cation with a water molecule is investigated computationally by coupled cluster and density functional theories. Several low-energy paths of the mechanism for dihydrogen production from H2O by the positively charged aluminum cluster are identified. This reaction involves the initial formation of the association complex, exothermic by 25 kcal/mol, followed by the water dissociation and H2 elimination major steps, yielding the Al6O(+) product oxide with either the nonplanar or planar structure. The H2O dissociation on Al6(+) is the rate-determining step. Of the paths probed, the one kinetically most preferred leads from the O-H bond dissociation transition state lying below the separated reactants to the immediate HAl6OH(+) intermediate of the "open" type and involves further the more compact intermediate from which H2 is eliminated. The other reaction paths explored involve the activation enthalpy (at 0 K) for the rate-determining step of less than 2 kcal/mol relative to the Al6(+) + H2O. Natural population analysis based charges indicate that forming of H2 along the elimination coordinate is facilitated by the interaction of the hydridic and protic hydrogens. For the kinetically most favorable route detected, the coupled cluster singles and doubles with perturbative triples (CCSD(T)) relative energies calculated with the unrestricted and restricted HF references are in a good agreement. This investigation is relevant specifically to the recent mass spectrometric study of the reactivity of Aln(+) with water by Arakawa et al., and it provides a mechanistic insight into the formation of the observed AlnO(+) product oxide with n = 6.
authors.affiliation: Faculty of Chemistry, Wroclaw University, F. Joliot-Curie 14, 50-383 Wroclaw, Poland.
authors.forename: Jerzy
authors.initials: J
authors.lastname: Moc