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The oxide chemistry of both dimeric and trimeric transition-metal cluster ions containing iron and cobalt was studied in the gas phase by using Fourier transform mass spectrometry (FTMS). The dimers Fez+, CoFe', and Co2+ react rapidly with ethylene oxide by sequentially abstracting two oxygen atoms, while the trimers FeCo2+ and C O~+ abstract up to three oxygen atoms from ethylene oxide. The dimers and trimers also react with dioxygen. In addition, the bimetallic carbonyl cations Fe2(C0)4+, COF~(CO)~+, and C O~( C O )~+ react rapidly with dioxygen by displacing all the carbonyls forming M'M02' exclusively. The trimetallic carbonyl cations FeCo2(COj5+ and C O~( C O )~+ react rapidly with dioxygen by displacing up to four carbonyls to generate M'M,(O),(CO),+ ( n = 1-3). These species undergo a subsequent reaction with dioxygen which displaces the remaining carbonyls to generate both M'M204+ and M' MZO3' . The M' MzO4' species subsequently transfers an oxygen atom to dioxygen to generate M'M203+ and presumably 03. No fragmentations were observed for collisional activation of the M'MO', while the M'M02+ species yielded M+ and M'MO' in low efficiency, the M'M203+ species yielded M+ and M'MO' in very low efficiency, and the M'M204+ species yielded M'M203+. Finally, the observed ion-molecule reactions yield Do(M'M+-O) > 119 kcal/mol, 204 kcal/mol C D0(M'M+-20) < 238 kcal/mol, Do(M'M2+-O) > 85 kcal/mol, Do(M'MzO'-O) > 85 kcal/mol, D0(M'M2O2+-O) > 85 kcal/mol, and D0(M'M203+-O) C 25.5 kcal/mol. These results suggest formation of bridged oxide species for M'MO', M'M02', and M'M203'.There is considerable interest in small transition-metal clusters' since they are important in a variety of processes including homogeneous nucleation2 and are of particular relevance to the study of catalytic a~t i v i t y .~ As a result, these clusters have been the focus of intense e~perimental"'~ and theoretical14 investigations yielding information on such physical properties as structure, electronic character, binding energy, ionization potential, and electron affinity.Due to their very nature, gas-phase ion techniques are ideally suited for studying size-selected metal cluster ions. Knudsen cell mass spectrometry has yielded bond energies for most homonuclear transition-metal dimers.15 Armentrout and co-workers have also demonstrated the utility of using an ion beam instrument to determine the bond energy of dimer ions by measuring their collision-induced dissociation thresholds.I6In general transition-metal cluster ions have been generated by either electron impact" or multiphoton ionization,'* typically on multinuclear carbonyl complexes. The former method, for example, has been employed for studying the gas-phase ion chemistry of Co2' l9 and Mnz+19-21 by ion cyclotron resonance (ICR) spectrometry and ion beam techniques. These ionization techniques, however, are quite limited as to both the size and stoichiometry of the bare transition-metal cluster ions which can be generated. Smalley'o and Bondybey" have recently developed elegant an...

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The gas-phase reactions of Y+ and La+ with linear, branched, and cyclic alkanes are reported. Dehydrogenation is predominant for ethane and propane while dehydrogenation and carbon-carbon bond cleavage occur for linear and branched alkanes larger than C3. As was observed for the other group 3 metal ion, Sc+, both Y+ and La+ form characteristic dialkyl ions. Evidence is given for two different YC4H6+ and LaC4H6+ isomeric structures. Reaction with cyclopropane gives predominant dehydrogenation products. The observation of LaCH2+ from cyclopropane implies D°(La+-CH2) > 93 kcal/mol. Only dehydrogenation products are observed for cyclopentane and cyclohexane. In general, the primary reactions of Y+ and La+ are found to be similar to those of Sc+. The secondary reactions of La+, however, are found to be considerably slower than those for Sc+ and Y+.

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