Near-threshold electron-impact excitation of argon studied with the time-of-flight technique

Abstract

Absolute angle-differential cross-section data are presented for excitation of the 3p 5 4s manifold in argon by electron impact. The investigation focuses on the near-threshold region, where previous studies have revealed persistent disparities between measurements and theoretical predictions. For the present experiment, the time-of-flight (TOF) technique is employed. This method allows for scattered electrons to be measured over a broad range of energies with a constant transmission, thereby eliminating a potential major source of error in relating relative intensities of elastic and inelastic transitions inherent to other experimental techniques. The present experimental data are compared to theoretical results obtained in relativistic distorted-wave and various Rmatrix (close-coupling) approaches, as well as to other recently published experimental data.PACS Codes: 34.80.Dp BackgroundThe accurate determination and understanding of electron-impact-induced atomic collision processes is important for a number of reasons. From a practical perspective, the modelling of many systems of environmental and technological interest relies on the incorporation of crosssection data to describe collision processes at the microscopic scale. These cross sections predict reaction rates for the range of possible collision outcomes comprising elastic scattering, excita- tion, and ionization. Thus the provision of precise cross-section data is vital to these applications. Sometimes, particularly in elastic scattering and excitation from the ground state, cross sections can be measured more accurately than they can presumably be calculated. On the other hand, measurements involving optically unstable initial states can be very difficult and are often impossible with currently available experimental techniques.Experimental benchmark data, therefore, may provide a crucial touchstone to both assess and to drive new developments in atomic collision theory and enhance its predictive powers. From a broader perspective, studies of electron-atom collisions contribute to our understanding of the electronic structure of matter by providing a well-defined testing ground to explore the manybody behaviour of many-electron systems.In the area of electron-atom collisions, the electron-noble-gas system has been a prime focus of study over many years. From the experimental perspective, these non-reactive gases can be easily handled and do not contaminate sensitive apparatuses. As a consequence, they are particularly conducive to the measurement of accurate cross-section data, which can assist in the development of theory for all atomic species, including those whose reactivity renders experiment infeasible. The present study concerns the excitation of argon atoms close to threshold, for which discrepancies between experiment and theory have persisted over a number of decades. Argon represents the most ubiquitous noble gas of the earth's atmosphere, comprising around 0.93% of its composition. It is used in a variety of applications includin...

Low-energy electron scattering from molecular hydrogen: Excitation of the X1Σg+ to bZawadzki1, Wright2, Dolmat3 et al. 2018Phys. Rev. A

“…However, their fixed θ limited the data that could be obtained. A later system capable of differential angles θ from 45 o to 130 o , with a higher energy resolution, energy-selected (60-80 meV, FWHM) pulsed electron beam was built by Buckman and coworkers [36] and was used to measure the excitation of He n = 2,3 levels at E 0 = 20.35 eV, 22.0 eV and 23.48 eV [37] as well as for Ar at 12.5 eV, 14 eV, 15 eV and 17.5 eV for θ from 55 o to 125 o [38] (see also [39]). Similarly as in [34]…”

Generalized oscillator strengths of the valence-shell excitations of argon studied by fast electron impact

“…The GOSs of the valence-shell excitations of argon were investigated by the electron energy loss spectroscopy (EELS) at low-energies [7][8][9][10] (<100 eV), moderate-energies [4,[11][12][13] (300-600 eV) and high-energies [4,[13][14][15][16][17][18][19] (1−25 keV) electron scattering. Among them, all the high-resolution studies at high impact electron energies [15,16,19] were carried out with the gas cell used, and the high target density in the gas cell results in the well-known double scattering or the so-called pressure effect [20], which may influence the accuracy of the measured GOSs, although the pressure effect has been corrected by extrapolating the measured results to the zero pressure.…”