Analysis of excitation and ionization of atoms and molecules by electron impact
This book treats selectively chosen subjects concerning the investigation of excitation and ionization of atoms and molecules by electron impact, namely: multiple ionization of rare-gas (He, Ar, Kr, and Xe) atoms and of H\(_2\), SO\(_2\), and SH\(_6\) molecules, measurements of partial and total double differential cross sections, electron impact excitation and polarization measurements for He I 3 \(^{1,3}\)P states of He, excitation function and polarization of the Ca II line of wavelength 393.3 nm and absolute cross section for the Ca II 4 \(^2P_1/2\) state of Ca, and polarization measurements for the excitation of the Sr I 5 \(^1\)P state of Sr and for the Na and K atoms. In the ``Introduction'' chapter, the authors briefly review the topics covered in the book. The next chapter, entitled ``Theoretical approaches'', introduces the measured physical quantities, e.g., partial and total double differential cross sections (PDDCS and DDCS, respectively) or Stokes polarization parameters, including also some basics about atomic transitions, and gives a short inventory of the theoretical models. The next two chapters, devoted to the experimental apparatus and techniques, contain a detailed presentation of the instrumentation and experimental methods used by the authors. A crossed-beam arrangement was used, where the focused beam of energetic electrons is allowed to interact with a beam of atoms or molecules emitted by the beam source (a capillary array for gases or an oven for Na, K, Ca, and Sr atoms). For the investigation of the ionization of atomic (He, Ar, Kr) and molecular (H\(_2\), SO\(_2\) and SF\(_6\)) gases, as well as the excitation of He, Ca and Sr atoms, electron analyzers and ion time-of-flight (TOF) analyzers or photon detectors have been introduced into ion-electron or photon-electron electronic coincidence circuits; in the case of Xe, an X-ray-ion electronic coincidence circuit was used. The parts of the experimental setup (electron and TOF ion analyzers, electron gun, atomic beam source, schematic electronic circuit, etc.) are presented in detail (some of them in great detail), and in some cases (e.g., the electron parallel-plate electrostatic analyzer, HPGe detector, crystal X-ray spectrometer, hexapole magnet, Langmuir-Taylor detector, etc.), the operation principles were also included. The rest of these chapters is devoted to the interesting information on the experimental technique for measurement of the polarization parameters of the induced fluorescent radiation in electron-polarized atom (Na, K, Ca, and Sr) collisions. Other basics, e.g. about atomic X-ray and electron spectra and fine and hyperfine structure of Na and K atoms, can also be found. The measurement results are collected in the chapter ``Results and discussion'' and presented especially in graphical form. Essentially, the applied experimental techniques and the results obtained in the present book correspond to the period preceding the dramatic technical developments showed by the field in the last two decades, driven by the invention of combined electric and magnetic projection techniques used along with imaging detectors (COLTRIMS or reaction-microscope techniques) -- see the collection of papers edited by \textit{J. Ullrich} in 2004 [Ten years of cold target recoil ion momentum spectroscopy and reaction microscopes. Max-Planck Institut für Kernphysik, Heidelberg (2004)]. Therefore, some of these experimental techniques and results (e.g., concerning DDCS data for simple systems) are out of date. However, besides the educational and historic interest, the book contains results that are currently topical. Thus, the PDDCS and DDCS data for rare-gas multiple ionization by electron impact show, among other trends, the role of Auger and Coster-Kronig transitions and of shake-off in the production of multiply ionized atoms. For example, an incident electron having an energy of 6 keV in a collision with Xe atoms can remove up to 9 electrons. New data of PDDCS and percentage branching ratios for the dissociative and non-dissociative ionization of H\(_2\), SO\(_2\), and SF\(_6\) molecules by electron impact were made available. In particular, the results are interesting for SO\(_2\) and SF\(_6\) molecules. For the SO\(_2\) molecule, the present data can add to the understanding of processes responsible for the dissociative ionization and consequent disappearance from the atmosphere of this air-polluting molecule. SF\(_6\) is a much-used gaseous dielectric, and the possibility of formation of harmful by-products by electron impact could be a serious problem. The present data can help to understand and overcome these difficulties. Also, the data obtained for polarization of fluorescence radiation from electron impact excitation of spin-polarized atoms of Na, K, Ca, and Sr and for excitation by electron impact of less studied states in He, Ca, and Sr atoms still could be of interest.
scientific article; zbMATH DE number 5768472