A comprehensive methodology for the study of sequential ion/molecule reactions using fourier transform ion cyclotron resonance the formation, isolation, and reactions of very large metal clusters

Abstract The focus of this paper is on the development and implementation of a comprehensive experimental methodology for the analysis of sequential ion molecule reactions using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS). This experimental methodology is applied to the synthesis of large metal carbonyl clusters and their gas-phase reactions with hydrocarbons. In a large cyclindrical ICR cell at 4.7 Tesla, low mass ions can undergo several hundreds of thousands of collisions before they escape from the trap. Sequential reactions consisting of over 20 consecutive reaction steps occur and the gas-phase polymerization reactions of metal carbonyls produce large metal-cluster ions containing up to 40 metal atoms. The application of selective collisional activation (CA) and collision-induced decomposition (CID) to unreactive intermediates permits the synthesis of unusual and very large metal carbonyl clusters. Rhenium carbonyl clusters are observed up to mass 8828 Daltons, with unit mass resolution for masses higher than 4000 Daltons. An extension of the standard sweep ion ejection method called FERETS (front-end-resolution enhancement using tailored sweeps) results in very high front-end resolution. FERETS isolates single ions from isotopic clusters at mass 1025 Daltons without accelerating the ion of interest. The front-end resolution normalized to mass 100 Daltons is approximately 10 500. After single ion isolation, the metal carbonyl clusters react with cyclohexane admitted through a pulsed-valve inlet. Unequivocal chemical assignments were possible without MS/MS due to the inherent high resolution of FT-ICR. The average mass accuracy obtained was 15 p.p.m. in the broadband mode and 1 p.p.m. in the high-resolution mode. The feasibility of 5 consecutive steps of MS/MS on metal carbonyl clusters is demonstrated with the following MS 5 sequence: EI — (isolation-reaction) — (isolation-CID) — (isolation-reaction) — (isolation-reaction) — (acceleration-detection).