Autoionization of N₂studied using an electron time-of-flight coincidence spectrometer

Autoionizing states of N 2 have been studied using a new electron-electron coincidence technique, by simultaneous measurement of their excitation energies and ejection energies in decay to states of N 2 + . This method gives a much clearer understanding of molecular autoionization than methods which measure either energy separately. Low energy electron impact is employed using hemispherical analysers to select the incident beam and to detect scattered electrons which have excited a selected autoionizing level. In coincidence with these scattered electrons, ejected electrons are analysed by measurement of their flight times along a field-free region. Transitions between the selected autoionizing level and levels of N 2 + appear as peaks in the time spectra. The design, construction and operation of the spectrometer are discussed and factors limiting the time and energy resolutions are considered. Results are presented showing time spectra for electrons ejected from five autoionizing states of N 2 and good agreement is observed between the predicted and measured resolutions of the spectrometer.