Abstract
A new spectrometer is described for measuring the momentum distributions of scattered electrons arising from electron-atom and electron-molecule ionization experiments. It incorporates and builds on elements from a number of previous designs, namely, a source of polarized electrons and two high-efficiency electrostatic electron energy analyzers. The analyzers each comprise a seven-element retarding-electrostatic lens system, four toroidal-sector electrodes, and a fast position-and-time-sensitive two-dimensional delay-line detector. Results are presented for the electron-impact-induced ionization of helium and the elastic scattering of electrons from argon and helium which demonstrate that high levels of momentum resolution and data-collection efficiency are achieved. Problematic aspects regarding variations in collection efficiency over the accepted momentum phase space are addressed and a methodology for their correction presented. Principles behind the present design and previous designs for electrostatic analyzers based around electrodes of toroidal-sector geometry are discussed and a framework is provided for optimizing future devices.
Highlights
A detailed understanding of electron-impact-induced ionization is essential to our understanding of a broad range of physical processes
We first provide a historical account of developments and explain the theoretical considerations for designing optimized electrostatic electron momentum analyzers based around electrodes of toroidal-sector geometry
By describing how we arrived at the present design, combining and building on the strengths of previous devices, we aim to provide a design framework for the optimization of future analyzer systems based around electrodes of toroidal-sector geometry
Summary
A detailed understanding of electron-impact-induced ionization is essential to our understanding of a broad range of physical processes. The simplest example of this process is provided by the single ionization of an isolated atomic species This process can be investigated experimentally by colliding electrons of well-defined momenta with isolated target atoms and measuring the momentum distributions of the reaction products. We first provide a historical account of developments and explain the theoretical considerations for designing optimized electrostatic electron momentum analyzers based around electrodes of toroidal-sector geometry. We present relative-cross-section data for elastic scattering ande , 2eionization processes These results demonstrate that while high levels of instrumental performance have been achieved, correcting for collectionefficiency variations in the measured angular distributions can be problematic. By describing how we arrived at the present design, combining and building on the strengths of previous devices, we aim to provide a design framework for the optimization of future analyzer systems based around electrodes of toroidal-sector geometry
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