QUANTITATIVE-DETERMINATION OF KINETIC-ENERGY RELEASES FROM METASTABLEDECOMPOSITIONS OF SPUTTERED ORGANIC IONS USING A TIME-OF-FLIGHT MASS-SPECTROMETER WITH A SINGLE-STAGE ION MIRROR

A method has been developed for determining the kinetic energy release d when metastable organic ions, produced by particle-induced desorptio n-ionization, decompose in a time-of-flight mass spectrometer having a single-stage ion mirror. To the best of our knowledge, this is the fi rst report of a fully developed, quantitative procedure for this parti cular 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 d etermined 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 wid ths of the precursor ion peak and the charged fragment ion peak are me asured respectively after both types of ion species have independently followed precisely the same flight path in space and time. With a sin gle-stage mirror, the latter condition is met by reflecting the precur sor and fragment ions with mirror potentials that are in proportion to the respective masses of the ions. Theoretical, experimental, and err or analyses are described and illustrated with examples.