Quantitative determination of kinetic energy releases from metastable decompositions of sputtered organic ions using a time-of-flight mass spectrometer with a single-stage ion mirror

Abstract

A method has been developed for determining the kinetic energy released when metastable organic ions, produced by particle-induced desorption—ionization, decompose in a time-of-flight mass spectrometer having a single-stage ion mirror. To the best of our knowledge, this is the first report of a fully developed, quantitative procedure for this particular combination of ionization method and mass analysis. In order to obtain the kinetic energy released in a specific metastable decay, the rate constant for the unimolecular reaction has to be estimated, and the widths of the precursor and charged fragment ion peaks have to be measured. The rate constant for a specific decomposition reaction is determined by deflecting all ions away from the optic axis at positions of increasing distance along the flight path through the first field-free region of the spectrometer and by counting the neutral fragments that reach the detector located at the back end of the mirror. The widths of the precursor ion peak and the charged fragment ion peak are measured respectively after both types of ion species have independently followed precisely the same flight path in space and time. With a single-stage mirror, the latter condition is met by reflecting the precursor and fragment ions with mirror potentials that are in proportion to the respective masses of the ions. Theoretical, experimental, and error analyses are described and illustrated with examples.