Construction and calibration of a custom time-of-flight mass spectrometer and its use in measuring the reaction kinetics of transition metal ion-organic interactions.

摘要

A unique instrument was constructed and used to generate and interrogate jet cooled neutrals, ions and their respective clusters. The instrument is a result of the artful marriage of supersonic expansions combined with time of flight spectroscopy. Ionization occurs in a large main chamber. The ions are separated via a kinetic energy pulse from a custom built linear particle accelerator. The revelatory hardware for our instrument is a microchannel plate detector (MCP). The MCP is mounted on the exit of a custom designed and built hemispherical energy analyzer (sector), which acts as an energy filter. This filtering characteristic of the sector permits study of selected ionized fragments.;To test the instrument, the 2-photon resonant, 3-photon ionization spectrum of gaseous atomic copper was measured. The 2D 5/23d10 nd ← S 1/23d10 4s (n = 9 -- 21) Rydberg series was observed in 2-photon excitation. The term energies of this series converged to copper's lowest ionization threshold with an apparent quantum defect of 0.92. The state which couples the ground 2S1/23d10 4s state of copper to the 2D 5/23d10 nd Rydberg series is a non-stationary state composed primarily of the spin-orbit components of the lowest 2P° atomic states.;Additionally, the time dependence of the gaseous unimolecular decomposition of the jet-cooled adduct ion, Ni+•Acetone was monitored by selective detection of the daughter fragment, Ni+CO. Various photon energies were supplied to initiate dissociation of the adduct ion. The energies employed in this reaction were well below that required to fragment C-C sigma-bonds. First-order unimolecular decomposition rate constants, k(E) ranged from 55000 -- 113000 s-1. The rate constants decreased with decreasing amounts of internal excitation. Ni + cation is implicated as a catalytic necessity to activate the bond and cause molecular fragmentation. These experiments represent the first direct kinetic study of such catalytic type reactions.