Unimolecular Decomposition in Ion Cyclotron Resonance Traps: Kinetic Energy Release and Microsecond-Scale Kinetics

Abstract

A method of recovering information about the kinetics and dynamics of gas-phase ion-molecule reactions which occur on a microsecond time scale inside a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR-MS) cell is presented. In FT-ICR experiments, the typical time-scale of the ion detection is of the order of milliseconds to seconds and the microsecond-scale reactions usually run to completion before the detection takes place. However, axial oscillation inside the ICR cell can be made very fast and the efficiency of the dynamic voltage trapping depends on the axial position of the ions. We present a theoretical model which relates experimental ion abundance to the life-times and kinetic energy releases, illustrating it with an example of fast-decomposing chromium hexacarbonyl molecular cation activated by collision with a fluorinated self-assembled monolayer surface in a 7-Tesla FT-ICR cell. General formalism, quantitative limitations and application of this method to measure lifetimes and the kinetic energy releases of less-studied ionic systems are addressed in detail.