Total Electron—Atom Collision Cross Sections at Low Energies—A Critical Review

Total absolute cross sections for electron scattering on hexafluorobenzene, C 6 F 6 , and sulfur hexafluoride, SF 6 , molecules, have been measured as a function of impact energy from 0.6 to 250 eV. The total cross section for C 6 F 6 exhibits a very broad peak stretching from 10 to 100 eV with some weak features near 9.5 and 15 eV superimposed on the peak. Apart from the well-known low-energy resonant structures in the SF 6 total cross section function, a new weak resonant feature close to 25 eV has been noticed in the present experiment, in accordance with earlier theoretical calculations.

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“…The method relates the cross section to the transparency of the target at a given pressure for a beam of projectiles (cf [14]). …”

Section: Methodsmentioning

confidence: 99%

Electron scattering on C6F6 and SF6 molecules

Kasperski

Możejko

Szmytkowski

1997

Z Phys D - Atoms, Molecules and Clusters

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“…Using the full quantum theory as well as the semiclassical approach, the elastic proton-hydrogen (H + + H) collision cross section σ in is calculated by Krstic & Schultz (1999), and its integral value at 0.5 eV is about 1.8 × 10 −18 m 2 for the elastic scattering, and about 10 −18 m 2 for the momentum transfer. As for the electron-hydrogen (e − + H) collisions, the collision cross section σ en is also temperature dependent and the corresponding values can be found in the works of Bedersen & Kieffer (1971), and Zecca et al (1996). At energies of 0.5 eV it is about 3.5 × 10 −19 m 2 , so that for the elastic scattering we have σ in /σ en 6.…”

Section: Physics Of Weakly Ionized Plasmasmentioning

confidence: 97%

Energy flux of Alfvén waves in weakly ionized plasma

Vranjes

Poedts

Pandey³

et al. 2007

A&A

106

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Context. The overshooting convective motions in the solar photosphere, resulting in the foot point motion of different magnetic structures in the solar atmosphere, are frequently proposed as the source for the excitation of Alfvén waves, which are assumed to propagate towards the chromosphere and corona resulting finally in the heating of these layers by the dissipation of this wave energy. However, the photosphere is a) very weakly ionized, and, b) the dynamics of the plasma particles in this region is heavily influenced by the plasma-neutral collisions. Aims. The purpose of this work is to check the consequences of these two facts on the above scenario and their effects on the electromagnetic waves. Methods. Standard plasma theory is used and the wave physics of the weakly ionized photosphere is discussed. The magnetization and the collision frequencies of the plasma constituents are quantitatively examined. Results. It is shown that the ions and electrons in the photosphere are both un-magnetized; their collision frequency with neutrals is much larger than the gyro-frequency. This implies that eventual Alfvén-type electromagnetic perturbations must involve the neutrals as well. This has the following consequences: i) in the presence of perturbations, the whole fluid (plasma + neutrals) moves; ii) the Alfvén velocity includes the total (plasma + neutrals) density and is thus considerably smaller compared to the collision-less case; iii) the perturbed velocity of a unit volume, which now includes both plasma and neutrals, becomes much smaller compared to the ideal (collision-less) case; and iv) the corresponding wave energy flux for the given parameters becomes much smaller compared to the ideal case. Conclusions. The wave energy flux through the photosphere becomes orders of magnitude smaller, compared to the ideal case, when the effects of partial ionization and collisions are consistently taken into account.

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“…This minimum is known to occur in an energy range of about 0·2-0·3 eV, which is close to the lower energy limit of single collision beam experiments (see e.g. Crompton 1969; Bederson and Kieffer 1971). In addition, the available cross sections for electron-argon atom collisions indicate that at energies at or near the minimum the cross section changes so rapidly with energy that even for an electron beam with an energy width of 10 meV the value of the cross section would vary by as much as 50 % within the energy range of the beam.…”

Section: Introductionmentioning

confidence: 98%

Drift Velocities of Low Energy Electrons in Argon at 293 and 90 K

Robertson¹

1977

Aust. J. Phys.

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The drift velocity of electrons in argon has been measured at 90 K in the range 0·002 ,;;; E/ N (Td) :.;; 0·7 and at 293 K in the range 0·01 ,;;; E/N (Td) ,;;; 1·0. The high sensitivity of the drift velocities to the presence of small quantities of diatomic impurities, particularly nitrogen, was demonstrated by adding known but trace quantities of diatomic gases. In this way it was observed that the presence of 6 p.p.m. nitrogen in the argon gave errors in the drift velocity of up to 3 %. As a result it was necessary to purify research grade gas before use. A full discussion is given of the errors incurred in the measurements.

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Total Electron—Atom Collision Cross Sections at Low Energies—A Critical Review

Cited by 237 publications

References 161 publications

Electron scattering on C6F6 and SF6 molecules

Electron scattering on C6F6 and SF6 molecules

Energy flux of Alfvén waves in weakly ionized plasma

Drift Velocities of Low Energy Electrons in Argon at 293 and 90 K

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