The ionization of inert gas atoms by electron and proton impact at high energies

Kingston, A E; Schram, B.L.; Heer, F. J. de

doi:10.1088/0370-1328/86/3/305

Cited by 15 publications

(4 citation statements)

References 21 publications

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“…This value is more than two orders of magnitude smaller than that for the isoelectronic HCl molecule (Neufeld & Wolfire 2009). A similar estimate of the ArH + photodissociation rate was obtained from the same theoretical cross-sections by Roueff et al (2014, in press) 6) The primary cosmic ray ionization rate for Ar is an order of magnitude larger than that for H (Kingston 1965;Jenkins 2013).…”

Section: Basic Features Of Argon Chemistrysupporting

confidence: 72%

Ubiquitous argonium (ArH⁺) in the diffuse interstellar medium: A molecular tracer of almost purely atomic gas

Schilke

Neufeld

Müller

et al. 2014

A&A

143

171

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Aims. We describe the assignment of a previously unidentified interstellar absorption line to ArH + and discuss its relevance in the context of hydride absorption in diffuse gas with a low H 2 fraction. The confidence of the assignment to ArH + is discussed, and the column densities are determined toward several lines of sight. The results are then discussed in the framework of chemical models, with the aim of explaining the observed column densities. Methods. We fitted the spectral lines with multiple velocity components, and determined column densities from the line-to-continuum ratio. The column densities of ArH + were compared to those of other species, tracing interstellar medium (ISM) components with different H 2 abundances. We constructed chemical models that take UV radiation and cosmic ray ionization into account. , and HF column densities promises to be a faithful tracer of the distribution of the H 2 fractional abundance by providing unique information on a poorly known phase in the cycle of interstellar matter and on its transition from atomic diffuse gas to dense molecular gas traced by CO emission. Abundances of these species put strong observational constraints upon magnetohydrodynamical (MHD) simulations of the interstellar medium, and potentially could evolve into a tool characterizing the ISM. Paradoxically, the ArH + molecule is a better tracer of almost purely atomic hydrogen gas than H itself, since H can also be present in gas with a significant molecular content, but ArH + singles out gas that is >99.9% atomic.

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Section: Basic Features Of Argon Chemistrysupporting

confidence: 72%

Ubiquitous argonium (ArH⁺) in the diffuse interstellar medium: A molecular tracer of almost purely atomic gas

Schilke

Neufeld

Müller

et al. 2014

A&A

143

171

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“…In the description of secondary ionizations in Section A.1, it was noted that at low electron energies the cross section for collisional ionization for Ar is about 3.85 times that of hydrogen. Accordingly, we find that Again, we used the results of Hooper et al (1962) and Kingston (1965) to find that ζ p,CR (He 0 )/ζ p,CR (H 0 ) = 1.36. Most of the secondary electrons are not energetic enough to ionize He, so Eq.…”

Section: (C2)mentioning

confidence: 95%

“…Again, we used the results of Hooper et al (1962) and Kingston (1965) to find that ζ p,CR (He 0 )/ζ p,CR (H 0 ) = 1.36. Most of the secondary electrons are not energetic enough to ionize He, so Eq.…”

Section: Cosmic Ray Ionizationmentioning

confidence: 99%

“…As with their susceptibility to ionization by photons, argon atoms are about 10 times more easily ionized by protons than hydrogen (for proton energies E ∼ 1 MeV) (Hooper et al 1962;Kingston 1965). In the description of secondary ionizations in Section A.1, it was noted that at low electron energies the cross section for collisional ionization for Ar is about 3.85 times that of hydrogen.…”

Section: (C2)mentioning

confidence: 99%

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The Fractional Ionization of the Warm Neutral Interstellar Medium

Jenkins

2013

ApJ

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When the neutral interstellar medium is exposed to EUV and soft X-ray radiation, the argon atoms in it are far more susceptible to being ionized than the hydrogen atoms. We make use of this fact to determine the level of ionization in the nearby, warm, neutral medium (WNM). By analyzing FUSE observations of ultraviolet spectra of 44 hot subdwarf stars a few hundred pc away from the Sun, we can compare column densities of Ar I to those of O I, where the relative ionization of oxygen can be used as a proxy for that of hydrogen. The measured deficiency [Ar I/O I] = −0.427 ± 0.11 dex below the expectation for a fully neutral medium implies that the electron density n(e) ≈ 0.04 cm −3 if n(H) = 0.5 cm −3 . This amount of ionization is considerably larger than what we expect from primary photoionizations resulting from cosmic rays, the diffuse X-ray background, and X-ray emitting sources within the medium, along with the additional ionizations caused by energetic secondary photoelectrons, Auger electrons, and photons from helium recombinations. We favor an explanation that bursts of radiation created by previous, nearby supernova remnants that have faded by now may have elevated the ionization, and the gas has not yet recombined to a quiescent level. A different alternative is that the low energy portion of the soft X-ray background is poorly shielded by the H I because it is frothy and has internal pockets of very hot, X-ray emitting gases.

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Commission des Donnees Spectroscopiques Fondamentales

Moore-Sitterly

1967

Reports on Astronomy/Proceedings of the Thirteenth General Assembly Prague 1967

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The ionization of inert gas atoms by electron and proton impact at high energies

Cited by 15 publications

References 21 publications

Ubiquitous argonium (ArH⁺) in the diffuse interstellar medium: A molecular tracer of almost purely atomic gas

Ubiquitous argonium (ArH⁺) in the diffuse interstellar medium: A molecular tracer of almost purely atomic gas

The Fractional Ionization of the Warm Neutral Interstellar Medium

Commission des Donnees Spectroscopiques Fondamentales

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The ionization of inert gas atoms by electron and proton impact at high energies

Cited by 15 publications

References 21 publications

Ubiquitous argonium (ArH+) in the diffuse interstellar medium: A molecular tracer of almost purely atomic gas

Ubiquitous argonium (ArH+) in the diffuse interstellar medium: A molecular tracer of almost purely atomic gas

The Fractional Ionization of the Warm Neutral Interstellar Medium

Commission des Donnees Spectroscopiques Fondamentales

Contact Info

Product

Resources

About

Ubiquitous argonium (ArH⁺) in the diffuse interstellar medium: A molecular tracer of almost purely atomic gas

Ubiquitous argonium (ArH⁺) in the diffuse interstellar medium: A molecular tracer of almost purely atomic gas