A neutral ZEKE beam: An approach for measuring ZEKE spectra

A technique is proposed for zero kinetic energy (ZEKE) spectroscopy that makes use of the long lifetime of neutral ZEKE states lasting for some 100 mu s in a long beam. Ionization of the ZEKE states is delayed downstream until just in front of the detector. As such, it eliminates the need for mu-metal shielding and will provide both highly resolved mass and ZEKE electron resolution. When ion detection techniques are used to obtain ZEKE spectra, the ions arising from the ZEKE states of interest must be separated from ions produced directly (background ions). However, the same spoiling fields necessarily used to discriminate ZEKE states also destroys them, via field induced ionization, and thus reduces signal. in the very long beam we demonstrate that the use of extremely small electric fields suffices to separate the ZEKE neutral states from the background ions. This is of crucial importance for large masses: This now will permit the analysis of very large molecules and electrons, both at high resolution.