Absolute angle-differential cross sections for electron-impact excitation of neon atoms from threshold to 19.5 eV

Abstract

Absolute angle-differential cross sections for electron-impact excitation of neon atoms to the four levels with the (2p 5 3s) configuration have been determined both experimentally and theoretically for incident energies from threshold up to 19.5 eV at scattering angles of 135 • and 180 • . Excellent agreement between the experimental data and theoretical predictions, obtained by a Breit-Pauli B-spline R-matrix method with non-orthogonal orbitals, has been found in terms of both absolute values and the energies and widths of the numerous resonant features.Absolute cross sections for inelastic electron scattering from rare-gas atoms are of great importance for gaseous discharge physics [1], but-except for helium-the theoretical description of these processes has remained a substantial challenge. Recently, however, significant progress has been made by means of a B-spline R-matrix method [2][3][4]. The key feature of this method is the possibility to use non-orthogonal sets of term-dependent one-electron orbitals. This allows for an accurate target description with relatively small configuration expansions. Excellent agreement was observed, for instance, between the calculated energy-dependent cross sections for the production of metastable Ne [2] and Ar [3] atoms with those measured in high-resolution experiments [5][6][7]. For Ne, a very sharp resonance (energy 18.527 meV, width 0.8 meV) was theoretically predicted [2] and subsequently confirmed experimentally [7].For thorough tests of theoretical approaches, it is highly desirable to compare the computed results with detailed experimental information, such as angle-differential excitation cross sections, obtained in absolute units at energies near threshold, where the excitation process is dominated by prominent resonance structure [5]. A particular point of interest is the coupling of the various anion resonances to specific final states. Apart from numerous work on He (see, e.g., [5,8,9]) and some results for Ar [5,6] and Kr [5,10], such data are currently missing in the literature.

Analysis of Optical Emission Spectroscopy on Discharges

“…Data for the electron impact excitation are available for neon [7]. The overall accuracy of cross sections in comparison to experimental data is high for the excitation to the lowest excited levels [8] but differs close to threshold energies. The rate coefficient, however, is less affected due to the integration over the energy distribution function.…”

Form-Free Reconstruction of an Electron Energy Distribution Function from Optical Emission Spectroscopy

“…For the electron excitation cross sections and Einstein coefficients, there exists an extensive and consistent dataset from B-spline Breit-Pauli R-Matrix (BSRM) close-coupling calculations [11,12]. These data are combined with those from the atomic line database NIST [13].…”

“…This is a reasonable choice, given that the energy dependence of the cross sections is often known more accurately than the absolute scale (see, for example, ref. [16]), thereby allowing for an efficient implementation in the model. The relative width (root mean-square-variance, rms, divided by expectation value) of the prior distributions for the scale parameters is listed in table 1.…”

“…The relative width (root mean-square-variance, rms, divided by expectation value) of the prior distributions for the scale parameters is listed in table 1. The numbers were chosen according to details of the BSRM calculations and the available independent experimental validations of the cross sections (see [11,12]). The uncertainty of the Einstein coefficients A i j is assessed by considering the results of the BSRM calculations in the length and the velocity form of the electric dipole operator.…”

Assessment of Electron Energy Distributions in Discharges by Optical Emission Spectroscopy

“…[12]. The overall accuracy of the cross sections in comparison to experimental data is high for the excitation to the lowest excited levels [13] but differs close to threshold energies. The rate coefficient, however, is less affected because of the integration over the energy distribution function.…”