title: Stable Stoichiometry of Gas-Phase Manganese Oxide Cluster Ions Revealed by Temperature-Programmed Desorption.
abstract: Temperature-programmed desorption (TPD) experiments were performed on gas-phase manganese oxide cluster ions, namely, Mn(n)O(m)(+) (n = 3-20) and Mn(n)O(m)(-) (n = 3-18). These cluster ions were prepared by laser ablation of a manganese rod in the presence of oxygen gas, and their composition was investigated using mass spectrometry. The composition of Mn(n)O(m)(±) distribution lies above the m = (4/3)n line. When the cluster ions were heated to 1000 K, Mn(n)O(m)(+) (m = (4/3)n + δ, with δ = -1, 0) and Mn(n)O(m)(-) (m = (4/3)n + δ, with δ = 0, 1) was found to be the predominant species, formed by thermal dissociation. These experimental findings indicate that the nascent manganese oxide clusters comprise robust Mn(n)O(m)(±) (m/n ≈ 4/3) and weakly bound excess oxygen atoms. On the basis of the TPD experiments, the oxygen-molecule release was identified as the main dissociation channel. The temperature dependence of O2 desorption was found to be similar among the clusters with the same oxygen excess or deficiency regardless of the number of Mn atoms. The threshold energy of O2 desorption was estimated for Mn4O(m)(+) (m = 6-11) and compared with bond dissociation energies calculated by density functional theory.
authors.affiliation: Department of Basic Science, School of Arts and Sciences, The University of Tokyo, Komaba, Meguro, Tokyo 153-8902, Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Koyama
authors.affiliation: Department of Basic Science, School of Arts and Sciences, The University of Tokyo, Komaba, Meguro, Tokyo 153-8902, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kudoh
authors.affiliation: Department of Basic Science, School of Arts and Sciences, The University of Tokyo, Komaba, Meguro, Tokyo 153-8902, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Miyajima
authors.affiliation: Department of Basic Science, School of Arts and Sciences, The University of Tokyo, Komaba, Meguro, Tokyo 153-8902, Japan.
authors.forename: Fumitaka
authors.initials: F
authors.lastname: Mafuné