Determination of Autoionization Lifetimes by Ion Cyclotron Reonances Linewidths

Abstract

The half‐width and half‐height for power absorption in the ICR spectrometer is shown to depend upon the time during which an ion absorbs power in the detection region of the instrument. In the case of negative ions, it is shown that autoionization can limit resolution, and conversely that the observed resolution for a given negative ion can be used to determine autoionization lifetimes. The SF6 − ion is observed in the ICR spectrometer, and a lifetime of ∼ 500 μsec is calculated for this ion. The C4F8 − ion is observed, and a lifetime of ∼ 200 μsec is calculated for that ion. The lifetimes are discussed with respect to other measured and calculated values, which show a wide variation, and it is suggested that the autoionization lifetimes may be strongly dependent on the energy of the impacting electrons. In this study, both ions are shown to be produced by electrons which are trapped in the ICR cell as opposed to being produced by beamelectrons.