The authors attempt to give a comprehensive discussion of observations of atomic negative-ion resonances throughout the periodic table. A review of experimental and theoretical approaches to the study of negative-ion resonances is given together with a consideration of the various schemes that are used for their classification. In addition to providing, where possible, tabulated data for the energies, widths, and symmetries of these states, the authors also attempt to highlight regularities in their behavior both within groups of the periodic table and along isoionic sequences.

Atomic negative-ion resonances

Electron transmission spectroscopy is utilized to determine the vertical electron affinities and to characterize the temporary anion states of a series of alternant hydrocarbons including benzene, naphthalene, anthracene, tetracene, styrene, and cis‐ and trans‐stilbene. The vibrational structure present in the low lying resonances is interpreted in light of the charge distributions of the temporarily occupied orbitals. The energies of the anion states are compared with the predictions of PPP, PPP‐CI, and HAM calculations, the pairing theorem and with the results from optical absorption measurements on the ground state anions in rigid glasses.

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Electron transmission study of the temporary negative ion states of selected benzenoid and conjugated aromatic hydrocarbons

We have applied the Breit–Pauli B-spline R-matrix method described earlier (J. Phys. B: At. Mol. Opt. Phys. 37 (2004) 2173) to the treatment of e–Ar collisions. An individually optimized, term-dependent set of non-orthogonal valence orbitals is used to account for the strong term dependence in the one-electron orbitals. Concentrating on the near-threshold regime for excitation of the 3p54s manifold, we obtain excellent agreement with benchmark experimental data for the production of metastable atoms and for excitation of the VUV-emitting J = 1 levels. A detailed partial-wave resolved resonance analysis shows that many of the structures listed by Buckman and Clark (Rev. Mod. Phys. 66 (1994) 539) are composed of overlapping resonances. These, together with their principal components and decay channels, are identified and, in some cases, alternative classifications are suggested.

http://iopscience.iop.org/article/10.1088/0953-4075/37/10/013/pdf

B-spline Breit?Pauli R-matrix calculations for electron collisions with argon atoms

Electron-atom and electron-molecule collisional cross sections are needed in the modeling and understanding of phenomena ranging from planetary atmosphere science to industrial applications of plasmas. This article reviews the Born approximation and phenomenological scaling approaches that provide accurate excitation cross sections over a range of electron impact energies. The methods are illustrated for a variety of atomic and molecular systems.

Scaled plane-wave Born cross sections for atoms and molecules

Absolute differential elastic and vibrational excitation cross sections have been measured for N2 in the scattering angle ranges starting between 0° and 20° and extending to 180°, at energies between 0.8 and 5 eV. The results agree with many previous measurements, in particular for angles around 90°, but discrepancies were found in some cases for angles close to 0° and 180°. Integral and momentum-transfer cross sections have been derived and compared with previous beam and swarm measurements. The procedures for determining the instrumental response function and for assuring optimal beam overlap over wide ranges of angles and energies are discussed.

https://doc.rero.ch/record/6691/files/allan_med.pdf

Measurement of the elastic and v = 0 ? 1 differential electron?N2 cross sections over a wide angular range

High energy-resolution spectra of electrons scattered elastically from helium, neon and argon atoms have been obtained as functions of scattering angle and of incident electron energy. In addition to the well known levels of the lowest configurations of the temporary negative ions (resonances), the authors observe structures at energies close to those of the (core)np5(n+1)s levels of neon and argon. These structures are attributed to resonances having configurations (core)np5((n+1)s(n+1)p3P). By calibration against features occurring at known energies in the elastic scattering spectra and also metastable excitation spectra they determine accurately the energies of the observed resonances.

https://iopscience.iop.org/article/10.1088/0022-3700/10/7/018/pdf

J N H Brunt

Papers

Resonance structure in elastic electron scattering from helium, neon and argon