Single and double ionisation of helium by H+, He2+and Li3+ions

Shah, M B; Gilbody, H B

doi:10.1088/0022-3700/18/5/010

Cited by 355 publications

(286 citation statements)

References 27 publications

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“…p , and total cross section σ tot p for production of He + . Experimental data for the ionization cross section: empty circles, Shah & Gilbody (1985). Data for the electron capture cross section: filled circles, Welsh et al (1967); diamonds, Shah & Gilbody (1985).…”

Section: Ionization Of He By Proton Impactmentioning

confidence: 99%

“…Experimental data for the ionization cross section: empty circles, Shah & Gilbody (1985). Data for the electron capture cross section: filled circles, Welsh et al (1967); diamonds, Shah & Gilbody (1985). Data for the total ionization cross section: crosses, Pivovar & Levchenko (1967); triangles, Puckett & Martin (1970); squares, DuBois et al (1984).…”

Section: Ionization Of He By Proton Impactmentioning

confidence: 99%

“…The cross section for this charge transfer reaction has been measured by Welsh et al (1967) and Shah & Gilbody (1985). The cross section has a maximum at E p ≈ 25 keV, where it is about one order of magnitude larger than the ionization cross section σ ion p (see Fig.…”

Section: Ionization Of He By Electron Capturementioning

confidence: 99%

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Cosmic-ray ionization of molecular clouds

Padovani¹,

Galli²,

Glassgold³

2009

A&A

356

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: Ionization Of He By Proton Impactmentioning

confidence: 99%

Section: Ionization Of He By Proton Impactmentioning

confidence: 99%

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Cosmic-ray ionization of molecular clouds

Padovani¹,

Galli²,

Glassgold³

2009

A&A

356

475

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“…Theory: black dashed line, eikonal molecular method, reaction (1); red dashed line, eikonal molecular method, reaction (2); black solid line, eikonal atomic method, reaction (1); red solid line, eikonal atomic method, reaction (2). Experiments: crosses, Berkner et al [60]; squares, Schryber [61]; full diamonds, Schwab et al [62]; full triangles, Shah and Gilbody [63]; inverted triangles, Shah et al [54]; triangles, Williams [64]; full inverted triangles, Stier and Barnett [51]; circles, Welsh et al [65]; diamonds, Rudd et al [52]; full circles, Martin et al [53]; plus signs, Allison [40].…”

Section: High Energy Collision (E > 100 Kev/u)mentioning

confidence: 99%

Charge transfer in proton–helium collisions from low to high energy

Loreau

Ryabchenko

Vaeck

2014

J. Phys. B: At. Mol. Opt. Phys.

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The cross section for charge transfer in proton-helium collisions has been computed in the energy range from 10 eV/u up to 10 MeV/u. Four different methods (full quantal time-independent and time-dependent methods, molecular and atomic basis set semi-classical approaches) valid in different energy regimes have been used to calculate the partial and total cross section for single-electron capture. The results are compared with previous theoretical calculations and experimental measurements and the different theoretical methods used are shown to be complementary for describing the charge transfer reaction. A fit of the cross section, valid for collision energies from 10 eV/u up to 10 MeV/u is presented based on these results.

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“…We acknowledge financial support from the Deutsche Forschungsgemeinschaft (DFG), [28]; full circles, Mergel et al [29]; open squares, Schmidt et al [30] …”

Section: Acknowledgementsmentioning

confidence: 99%

Two-dimensional electron-momentum distributions for transfer ionization in fast proton-helium collisions

et al. 2013

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The momentum distribution of the electron in the reaction p+He → H + He 2+ + e is measured for projectile energies E p =300 and 630 keV/u at very small scattering angles of hydrogen. We mainly present two dimensional distributions parallel (k || ) and perpendicular (k ⊥ ) to the projectile beam. Theoretical calculations were carried out within the Plane Wave First Born Approximation (PWFBA), which includes both electron emission mechanisms, shake-off and sequential capture and ionization. It is shown that electron correlations in the target wave function play the most important role in the explanation of experimentally observed backward emission. Second order effects have to be involved to correctly describe the forward emission of the electron. * Electronic address: schoeffler@atom.uni-frankfurt.de 2

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Single and double ionisation of helium by H⁺, He²⁺and Li³⁺ions

Cited by 355 publications

References 27 publications

Cosmic-ray ionization of molecular clouds

Cosmic-ray ionization of molecular clouds

Charge transfer in proton–helium collisions from low to high energy

Two-dimensional electron-momentum distributions for transfer ionization in fast proton-helium collisions

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