Single and double ionization of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>by electrons and protons

Edwards, A. K.; Wood, R. M.; Beard, A.S.; Ezell, R.L.

doi:10.1103/physreva.37.3697

Cited by 47 publications

(14 citation statements)

References 16 publications

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“…The cross section for this reaction is highly uncertain: the measurements by Edwards et al (1988) and Kossmann et al (1990) disagree by a factor of ∼8. Here we adopt the latter set of measurements (shown in Fig.…”

Section: Dissociative Ionization Of H 2 By Electron Impactmentioning

confidence: 99%

Cosmic-ray ionization of molecular clouds

Padovani¹,

Galli²,

Glassgold³

2009

A&A

360

475

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Context. Low-energy cosmic rays are a fundamental source of ionization for molecular clouds, influencing their chemical, thermal, and dynamical evolution. Aims. The purpose of this work is to explore the possibility that a low-energy component of cosmic rays, not directly measurable from the Earth, can account for the discrepancy between the ionization rate measured in diffuse and dense interstellar clouds. Methods. We collected the most recent experimental and theoretical data on the cross sections for the production of H + 2 and He + by electron and proton impact and discuss the available constraints on the cosmic-ray fluxes in the local interstellar medium. Starting from different extrapolations at low energies of the demodulated cosmic-ray proton and electron spectra, we computed the propagated spectra in molecular clouds in the continuous slowing-down approximation taking all the relevant energy loss processes into account. Results. The theoretical value of the cosmic-ray ionization rate as a function of the column density of traversed matter agrees with the observational data only if the flux of either cosmic-ray electrons or of protons increases at low energies. The most successful models are characterized by a significant (or even dominant) contribution of the electron component to the ionization rate, in agreement with previous suggestions. However, the large spread of cosmic-ray ionization rates inferred from chemical models of molecular cloud cores remains to be explained. Conclusions. Available data combined with simple propagation models support the existence of a low-energy component (below ∼100 MeV) of cosmic-ray electrons or protons responsible for the ionization of molecular cloud cores and dense protostellar envelopes.

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Section: Dissociative Ionization Of H 2 By Electron Impactmentioning

confidence: 99%

Cosmic-ray ionization of molecular clouds

Padovani¹,

Galli²,

Glassgold³

2009

A&A

360

475

View full text Add to dashboard Cite

show abstract

“…1) can be separated from ground-state dissociation (channels 2b and 2c) using the fact that the kinetic energy of the H + from the former is typically of the order of a few eV, whereas from the latter it is in the sub-eV range [18]. Until now the experiments focused either on electron emission characteristics [8,9,12] or on the measurement of the nuclear fragments only [10,11].…”

mentioning

confidence: 99%

Breakup ofH2in Singly Ionizing Collisions with Fast Protons: Channel-Selective Low-Energy Electron Spectra

et al. 2004

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Dissociative as well as nondissociative single ionization of H2 by 6 MeV proton impact has been studied in a kinematically complete experiment by measuring the momentum vectors of the electron and the H+ fragment or the H+2 target ion, respectively. For the two ionization pathways, the electron spectra reveal the role of autoionization of the doubly and singly excited states of H2. The latter explicitly involve the coupling between the electronic and the nuclear motion of the molecule. This is a clear manifestation of a breakdown of the Born-Oppenheimer approximation.

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“…In this article we report measurements of DDCS for ionization accompanied by fragmentation (IF) of H 2 by 75 keV proton impact, which leads to at least one positively charged fragment. Several channels contribute to IF and most of them proceed through the two-electron processes of double excitation followed by auto-ionization, ionization-excitation, and double ionization [17,18]. The only one-electron process that can lead to IF is single ionization accompanied by vibrational excitation of the molecule [10,18].…”

Section: Introductionmentioning

confidence: 99%

Scattering-angle dependence of doubly differential cross sections for fragmentation ofH2by proton impact

et al. 2011

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We have measured double differential cross sections (DDCS) for proton fragment formation for fixed projectile energy losses as a function of projectile scattering angle in 75 keV p + H 2 collisions. An oscillating pattern was observed in the angular dependence of the DDCS with a frequency about twice as large as what we found earlier for nondissociative ionization. Possible origins for this frequency doubling are discussed.

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Single and double ionization ofH2by electrons and protons

Cited by 47 publications

References 16 publications

Cosmic-ray ionization of molecular clouds

Cosmic-ray ionization of molecular clouds

Breakup ofH2in Singly Ionizing Collisions with Fast Protons: Channel-Selective Low-Energy Electron Spectra

Scattering-angle dependence of doubly differential cross sections for fragmentation ofH2by proton impact

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