title: Reactions of cationic iron clusters with ammonia, models of nitrogen hydrogenation and dehydrogenation.
abstract: The gas phase reactivities of small cationic iron clusters, Fen+ (n = 1-20), towards ammonia were investigated using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Sequential addition of ammonia molecules to the clusters was observed to be the dominating process for n > 4. In the case of n = 4 we observed addition of ammonia accompanied by dehydrogenation. This reaction was modelled using hybrid density functional theory. Clusters with n < 4 do not react with ammonia. Clusters Fen+ (n = 1-20) react with neither N2 nor H2 at around 10(-8) mbar. When dinitrogen was seeded into the expanding helium, mixed clusters of the type FenNm+ were observed. These ions react with H2, either by addition, or by substitution of N2. The clusters with m = 1 were isolated in separate experiments and reacted with H2, which showed that mixed clusters with n = 5-13 add up to 5 molecules of dihydrogen in successive slow reactions.
authors.affiliation: Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway.
authors.forename: Kjell O
authors.initials: KO
authors.lastname: Fossan
authors.forename: Einar
authors.initials: E
authors.lastname: Uggerud