Dissociation rates of energy-selected benzene cations: comparison of experimental results from ion cyclotron resonance and cylindrical ion trap time-of-flight mass spectrometry

Abstract

Millisecond decay rates of the perdeuterio benzene cation (C 6D 6 +) are measured in two different ion storage equipments. Resonance-enhanced two photon ionization with a single laser beam leads to the production of the perdeuterio benzene cations without internal energy. By absorption of a third photon from the same laser or a second laser beam the ions are excited to internal energies of 4.64 eV and the decay rate is measured by the time dependent appearance of the C 6D 5 + and C 6D 4 + fragment within the electro-magnetic trap (Penning trap) of an ion cyclotron resonance (ICR) mass spectrometer and an electrodynamical ion trap (Paul trap) incorporated in a reflectron time-of-flight mass spectrometer. After correction for infrared relaxation we obtain a unimolecular decay rate constant of 1.15 × 10 3 s −1. We perform RRKM calculations for this experimental result and for previous values achieved from decay rate measurements in a reflectron mass spectrometer. They are in good agreement with the experimental dependence of decay rate constants for benzene (C 6H 6 +) and perdeuterio benzene cations (C 6D 6 +) over a wide range of decay rate constants between 10 3 and 2 × 10 6 s −1.