2 pi gas phase multichannel electron momentum spectrometer for rapid orbital imaging and multiple ionization studies

A 2 pi gas phase multichannel electron momentum spectroscopy (EMS) spectrometer with high sensitivity has been designed and constructed. The spectrometer employs symmetric non-coplanar geometry. A 90 degrees sector, 2 pi spherical electrostatic analyzer is used to energy select ionized and scattered electrons emanating from electron impact events in the collision chamber at a polar angle theta equal to 45+/-0.7 degrees. Azimuthal (p) angles are sampled around almost all of the available 360 degrees range. Four sets of multichannel position sensitive detectors, each consisting of two microchannel plates and a resistive anode encoder, are installed in four quadrants above the exit aperture of the analyzer. Electrons corresponding to a binding energy range of 38 eV and an azimuthal (p) angular range of 0 to +/-44 degrees are detected with time correlation (i.e. coincidence). Results for calibration of the system using elastic scattering and also inelastic scattering are reported. Preliminary EMS experiments on argon for binding energy spectra, angular distributions and momentum distributions are also presented. The results of pilot experiments employing electron to photon conversion as a basis for a new higher coincidence count rate, time correlated position sensitive detection system are also reported. Further applications of this instrumentation to multiple ionization electron spectroscopies using electron (2(+) and 3(+)) and photon (2(+), 3(+) and 4(+)) impact are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.