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) spectrom eter with high sensitivity has been designed and constructed. The spectrome ter employs symmetric non-coplanar geometry. A 90 degrees sector, 2 pi sphe rical electrostatic analyzer is used to energy select ionized and scattered electrons emanating from electron impact events in the collision chamber a t a polar angle theta equal to 45+/-0.7 degrees. Azimuthal (p) angles are s ampled around almost all of the available 360 degrees range. Four sets of m ultichannel position sensitive detectors, each consisting of two microchann el plates and a resistive anode encoder, are installed in four quadrants ab ove 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 deg rees are detected with time correlation (i.e. coincidence). Results for cal ibration of the system using elastic scattering and also inelastic scatteri ng are reported. Preliminary EMS experiments on argon for binding energy sp ectra, angular distributions and momentum distributions are also presented. The results of pilot experiments employing electron to photon conversion a s 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 elect ron (2(+) and 3(+)) and photon (2(+), 3(+) and 4(+)) impact are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.