Electron-molecule scattering cross-sections. I. Experimental techniques and data for diatomic molecules

Ar eview of the best-available data for calculating a complete set of binary collision integral data for the computation of the mixture transport properties (viscosity, thermal conductivity, and ordinary and thermal diffusion) of 13-species weakly ionized air is presented. Although the fidelity of the data varies, all collision integrals presented herein, except for electron-neutral interactions, are estimated to be accurate to within 25% over the temperature range of interest (300‐15,000 K) for reentry and laboratory plasmas. In addition, most of the dominant atom‐atom and atom‐ion interactions for dissociated weakly ionized air were derived from ab initio methods that are estimated to be accurate to within 10%. The accuracy and valid temperature range for electron-neutral interactions vary because of scarcity of the required cross-sectional data.

Recommended Collision Integrals for Transport Property Computations Part 1: Air Species

Cross section data are collected and reviewed for electron collisions with carbon monoxide. Collision processes included are total scattering, elastic scattering, momentum transfer, excitations of rotational, vibrational and electronic states, ionization, and dissociation. For each process, recommended values of the cross sections are presented, when possible. The literature has been surveyed through to the end of 2013.

Cross Sections for Electron Collisions with Carbon Monoxide

The substantial progress that has occurred during the 1990s in the field of electron-atom-collision theory is discussed. We show how a solution of a small-model three-body problem, using the convergent close-coupling method, has led to numerous applications involving real atomic collision systems. Consequently many fundamental electron-atom collision processes are considered as 'solved', and accurate collision data of interest to science and industry have become available. However, we suggest that the present has only just seen the birth of modern atomic collision theory. There are many more important collision problems to be tackled, with guidance coming from experiment being as important as ever.

https://iopscience.iop.org/article/10.1088/0953-4075/35/15/201/pdf

Electrons and photons colliding with atoms: development and application of the convergent close-coupling method

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

Procedures and calibration techniques for measuring the absolute elastic and inelastic differential cross sections (DCS) for electron impact on molecular (atomic) species are described and illustrated by examples. The elastic DCS for the molecule under study is first determined by calibration against helium using the relative flow technique. The second step involves the production of energy-loss spectra for the instrument response function, the unfolding of overlapping inelastic structures and the normalization of inelastic intensities to the elastic cross sections. It is concluded that this method of determining absolute differential electron-molecule (atom) scattering cross sections is generally applicable and provides reliable results.

https://iopscience.iop.org/article/10.1088/0022-3735/22/9/010/pdf

Principles and procedures for determining absolute differential electron-molecule (atom) scattering cross sections

We have measured the differential and integral cross sections for electron impact excitation of the , , and states of CO in the 10-15 eV impact energy region. These measurements fill the gap which existed between the low-energy (threshold to about 12 eV) data of Zobel et al and the intermediate energy (20-50 eV) results of Middleton et al. Recent electron time-of-flight measurements are utilized to place the relative cross sections (deduced from energy-loss spectra) on the absolute scale. The cross sections are in excellent agreement with the results obtained by Zobel et al at the overlapping impact energies and always smoothly extrapolate to their low-energy results. Extrapolation to the intermediate energy domain and comparison with the results of Middleton et al is not so clear. Comparison with theoretical differential and integral cross sections of Sun et al and the integral cross sections of Morgan and Tennyson reveals angular and energy dependences which resemble those found for the experimental results but there are serious discrepances concerning the absolute magnitudes.

Electron impact excitation of the , , and states of CO at 10.0, 12.5 and 15.0 eV impact energies

The results of a combined experimental and theoretical study of elastic electron scattering by laser-excited atoms are presented. From these studies, we extracted differential scattering cross sections and parameters for elastic scattering both by coherently prepared Ba atoms and by Ba atoms in an isotropic, incoherent state of the level. This is the first time that results of this type have been reported for elastic scattering by excited atoms. Good agreement was found between the limited experimental results and those obtained from our convergent close-coupling (CCC) theoretical calculations. It was demonstrated that elastic scattering can create alignment with significant probability.

Inelastic electron scattering by laser-excited atoms

Electron-impact excitation of the (...6s5d 1 D 2 ) to (...6s6p 1 P 1 ) transition in barium

Differential cross sections (DCS) and electron impact coherence parameters (EICP) have been measured and calculated for the (...6s6p 3PJ) levels in ytterbium. DCS for the (...6s6p 3P1) and (...6s6p 3P2) levels were determined at collision energies of 10, 20 and 40 eV. EICP for the (...6s6p 3P1) intermediate-coupled level were determined at collision energies of 20 and 40 eV. Calculations were made in the unitarized distorted-wave approximation. Measurements were made in a crossed-beam apparatus with EICP measured using the technique of superelastic scattering from atoms laser-excited into the 3P1 level.

P W Zetner

Papers

Principles and procedures for determining absolute differential electron-molecule (atom) scattering cross sections

Electron impact excitation of the , , and states of CO at 10.0, 12.5 and 15.0 eV impact energies

Inelastic electron scattering by laser-excited atoms

Electron-impact excitation of the (...6s5d 1 D 2 ) to (...6s6p 1 P 1 ) transition in barium

Electron impact excitation of the (..6s6p 3 P J ) levels in ytterbium.