The role of cluster ion structure in reactivity and collision-induced dissociation: Application to cobalt/oxygen cluster ions in the gas phase

Abstract

Ion/molecule reaction products of cobalt cluster ions have been characterized using mass spectrometric techniques. Atomic and bare-metal cluster ions were desorbed from foils by particle bombardment within a high-pressure (0.1–0.2 Torr) ion source. Sputtered metal cluster ions react with O2 to produce abundant stoichiometric or nearly stoichiometric cobalt(II) oxide cluster ions. The positive cluster product ions consist of three types: oxygen-deficient [Co(CoO)x]+ clusters, oxygen-equivalent [(CoO)x]+ clusters, and (in less abundance) metal-deficient [(CoO)xO]+ clusters. Tandem mass spectrometry and collision spectroscopy provide structural information about the more abundant cobalt cluster product ions. A major collision-induced fragmentation pathway for the oxygen-equivalent [(CoO)x]+ clusters is the loss of a CoO moiety to form [(CoO)x−1]+ fragments. A major collision-induced fragmentation pathway for the oxygen-deficient [Co(CoO)x]+ clusters is the loss of a cobalt atom to yield [(CoO)x]+ fragments. Geometric structures of the cobalt/oxygen cluster ions were calculated using a Coulomb plus Born–Mayer pair-potential model. The oxygen-equivalent cluster structures were found to be ‘‘globular’’ cages, rings, or ladders. The oxygen-deficient cluster structures were found to be strained and ‘‘angular’’ with protruding cobalt atoms. The structures are discussed in terms of the observed collision-induced fragmentations. The fragmentations are rationalized using an ‘‘instantaneous’’ dissociation model of the collision-induced dissociation of the cluster ions. Preliminary trajectory calculations using classical dynamics support the use of this instantaneous dissociation model. The role of cluster ion structure in reactivity and collision-induced dissociation is discussed in terms of the experimental data and theoretical structures.

Guided ion-beam studies of the reactions of Con+ (n=2–20) with O2: Cobalt cluster-oxide and -dioxide bond energies

“…For example, cobalt is known to be an important catalytic metal in many industrial processes, 1 including Fischer-Tropsch synthesis, in which larger hydrocarbons are produced from synthesis gases ͑CO and H 2 ͒. Freas et al 12 investigated the reactions of cobalt cluster cations with O 2 and collision-induced dissociation ͑CID͒ of cobalt oxides in a chemical ionization/fast atom bombardment source. 4 Cobalt-based alloys are often utilized as they are wear resistant, corrosion resistant, and heat resistant.…”

“…In this regard, the reactions of Fe, 5 Cr, 6 V, 7 and Ni ͑Ref. 12,13 In addition, Pramann et al 17 have examined anionic cobalt cluster oxides, Co n O m − ͑n =4-20 9͒ and Cr ͑Ref.…”

Quantum mechanical calculations of stoichiometric MgO clusters

“…This fragmentation path has been observed to be a major dissociation channel in CIF studies of small MgO clusters [4]. The loss of a neutral metal oxide monomer has also been reported as the preferred pathway for stoichiometric CoO cluster ions [1]. The calculated values are plotted in Fig.…”

“…In the last few years, there has been an intense interest in the study of binary metal oxide clusters [1][2][3][4][5][6][7][8][9] including mass spectra [3][4][5][6] and collision induced fragmentation (CIF) [4] data, classical simulations [5,6], and ab initio calculations [6][7][8][9] on MgO clusters. The abundance maxima in the mass spectra of (MgO)n ÷, (MgO),Mg ÷ (n<90), and (MgO),Mg2 + (n=4-172) are interpreted using pair-wise potential models by Ziemarm and Castleman [5,6].…”

Chemistry and kinetics of size-selected cobalt cluster cations at thermal energies. 2. Reactions with oxygen

“…34 The most abundant clusters were [Co(CoO),]+ and [(COO),]+ clusters. Financial support by the Environmental Protection Agency, Grant R-8 17437-01-0, and DuPont Chemicals through an unrestricted grant to the Department of Chemistry of The Pennsylvania State University, are gratefully acknowledged.…”