The transmission of electrons by gases

Abstract

This thesis is concerned with the measurement of total electron-atom and electron-molecule collision cross-sections and their interpretation, and the observation of fine structure in the transmitted current due to resonance processes. The definitions of total cross-section and related observable parameters are discussed. We then review the methods that have been used to observe electron transmission in gases and the cross-sections that have been reported in the literature. The interpretation of the features of the total cross-section function is discussed In terms of theoretical models. We consider classical mechanical models, wave mechanical models, and correlations based upon the similarity of chemical structures. Fine structure is considered in terms of modern resonance theory. From these considerations we outline the design requirements of an electron transmission spectrometer. A practicable design procedure using computer calculations of electron optical parameters lis described. This is then used to construct a spectrometer which will operate in the electron energy range 2-100 eV with a nearly constant background current, and with an energy resolution of about 0.050 eVe. The operating characteristics of the apparatus are described and an investigation of helium reported. We present total cross-section data for helium in the region 2-30 eV and compare them with published data. Our results, the first total cross-sections recorded in a non-magnetic electron spectrometer, deviate somewhat at higher energies from previously published cross-sections. We also record the resonances at 19.3 eV in helium and 1. 8-5.0 eV in nitrogen.