Ionization plus excitation of helium by fast electron and proton impact

Fülling, S.; Bruch, R.; Ea, Rauscher; Pa, Neill; Ph, Heckmann; McGuire, J. H.

doi:10.1103/physrevlett.68.3152

Cited by 35 publications

(8 citation statements)

References 33 publications

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“…When a negatively or positively charged projectile collides with a helium atom at intermediate to high impact energies, the dominant collision mechanisms are elastic scattering, excitation, and ionization of the target with subsequent emission of photons and/or electrons (Fülling et al 1992, Bailey et al 1995, Stolte and Bruch 1996. Simultaneous ionizationexcitation of the target can also occur at sufficiently high energies, but it leads to relatively small emission cross sections (Bailey et al 1995), thereby making this process very difficult to observe experimentally.…”

Section: Introductionmentioning

confidence: 99%

Ionization–excitation of helium to He(2p) magnetic sublevels following electron, proton, and molecular hydrogen (H₂and H₃) impact

Merabet

Bruch

Fülling

et al. 2003

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

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Experimental magnetic sublevel scattering-angle-integrated cross sections following ionization-excitation of He(1s 2) 1 S to He + (2p) 2 P o in e − + He and H + m +He (m = 1-3) collision systems have been determined using a combination of total cross sections and polarization fraction measurements in the extreme ultraviolet range. The derived magnetic sublevel cross sections, σ 0 and σ 1 , for M L = 0 ± 1 have been studied over a wide range of velocities (2-8.5 au) for electron impact on helium. These results are compared with previous experimental proton cross sections (2-6 au) as well as new measured data for hydrogen molecular impact (1.4-4.0 au) for equi-velocity. In addition, our electron and proton measurements are compared with earlier theoretical predictions, our recent second-Born calculations fully including off-shell energy terms, and present predictions from a hybrid first-order and second-order distorted-wave plus R-matrix (close-coupling) model (DWB1 + RMPS and DWB2 + RMPS). Finally, we have extended our polarization measurements for H + + He collisions and found excellent agreement between theory and experiment at nearly all impact energies. However, the present second-Born and DWB1 + RMPS results deviate slightly from the experimental electron data while the DWB2 + RMPS calculations tend toward the experimental data of Forand et al (1985

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Section: Introductionmentioning

confidence: 99%

Ionization–excitation of helium to He(2p) magnetic sublevels following electron, proton, and molecular hydrogen (H₂and H₃) impact

Merabet

Bruch

Fülling

et al. 2003

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

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“…1-2 These many-body aspects of atomic collision processes are associated with electron-electron correlations and other few-body dynamical phenomena that supercede independent-particle models. Most experiments have focused on two-electron mechanisms in helium, since this is the simplest target containing more than one electron, and it is therefore ideally suited for achieving a better theoretical understanding of the few-body problem [3][4][5][6][7][8][9][10][11] that is likely to be useful for the description of other complex systems, e.g. the dynamic behavior of atoms in molecules.…”

Section: Introductionmentioning

confidence: 99%

Polarization measurements of the extreme ultraviolet (EUV) emission following excitation and ionization-excitation of helium by fast electron, proton, and molecular hydrogen (H 2 + and H 3 +) impact

Merabet¹,

Bruch²,

Fuelling³

et al. 2002

SPIE Proceedings

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We report intensive experimental and theoretical data corresponding to helium extreme ultraviolet (EUV) emission in the 30-60 nm wavelengths range for e -+ He, H + + He, and H n + + He (n=2-3) collisions with impact velocities from 1.4 to 8.5 a.u. Specifically, the degree of linear polarization associated with HeI (1snp) 1 P o levels, n=2-5, (λ=51.7 to 58.4 nm for n=2-5 to n=1 transitions) and HeII (2p) 2 P o states (λ=30.4 nm) have been measured at intermediate-to high-energy range using a compact lightweight molybdenum/silicon multilayer mirror polarimeter (MLM). The combination of these polarization measurements with our previous total EUV cross sections has enabled us to determine experimental magnetic substate scattering angleintegrated cross sections, 0 σ and 1 σ for M L = 0, ±1, following excitation of He (1s 2 ) 1 S to HeI (1s2p) 1 P o levels and ionizationexcitation to He + (2p) 2 P o for electron and proton impact at a wide range velocities. The degree of linear polarization and obtained magnetic sublevel cross sections are compared to earlier theoretical calculations together with our recent 23-state RMatrix, 1 st and 2 nd Born calculations. Such a detailed comparison may shed more light on the collision processes involved in positively and negatively single-charge particle impact in helium. In particular it shows that electron-electron interactions play an important role in the ionization-excitation mechanism. In addition, this comprehensive database will possibly provide a deeper understanding of electron and proton induced jets in solar flare astrophysical investigations.

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“…In particular, the determination of electron and proton beam velocities and the related energy transfer mechanisms in solar flares of the chromospheric region strongly depends on hydrogen and helium polarization measurements [1][2] . Therefore it is ideally suited for detailed study of collision dynamics and correlation effects [5][6][7][8] . Consequently, laboratory and astrophysical spectropolarimeteric techniques based on s uch He EUV line emission may provide an excellent diagnostic tool for solar flare investigations.…”

Section: Introductionmentioning

confidence: 99%

<title>Spectropolarimetric measurements of the extreme-ultraviolet emission from helium following e-, H<formula><roman>+</roman></formula>, H2<formula><roman>+</roman></formula>, andH<formula><inf><roman>3</roman></inf></formula><formula><roman>+</roman></formula> charged particle impact</title>

et al. 2001

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We present here comprehensive experimental data corresponding to helium extreme ultraviolet emission (EUV) for the 300-600 Å wavelength range in e -+ He, H + + He, and H n + + He (n=2-3) collisions with impact velocities ranging from 1.4 to 6.9 a.u. The degree of linear polarization associated with HeI (1snp) 1 P o 2 S transitions (λ=304 Å), have been measured at intermediate and higher energies. These measurements have been conducted using a compact lightweight molybdenum/silicon multilayer mirror (MLM) spetropolarimeter. These experimental results are compared with our most advanced theoretical calculations using the close coupling method and several many body perturbation approaches. In this study, the degree of linear polarization will be discussed as a function of the projectile charge to elucidate few body excitation and ionization-excitation processes. Specifically, more sophisticated calculations including second Born approximation with full off-energy terms for the HeII (2p) 2 P o sublevels have been used. The excellent agreement with our HeII Lyman-α data clearly demonstrates that off-energy terms in two-electron atomic interaction have very prominent effects. Our comprehensive experimental and theoretical database is also of great importance for the understanding of solar physics phenomena. Such results can be used as a new diagnostic tool for clarifying the role of electron and proton beams in solar flares. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/21/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Proc. SPIE Vol. 4498 209 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/21/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

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Ionization plus excitation of helium by fast electron and proton impact

Abstract: We report the first experimental results on the state selective cross-section ratio a + /a of helium for electron and proton impact. Our results show consistently higher yields for electrons than for protons at higher velocities. A comparison is made between the cross-section ratios

Cited by 35 publications

References 33 publications

Ionization–excitation of helium to He(2p) magnetic sublevels following electron, proton, and molecular hydrogen (H₂and H₃) impact

Ionization–excitation of helium to He(2p) magnetic sublevels following electron, proton, and molecular hydrogen (H₂and H₃) impact

Polarization measurements of the extreme ultraviolet (EUV) emission following excitation and ionization-excitation of helium by fast electron, proton, and molecular hydrogen (H 2 + and H 3 +) impact

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Ionization plus excitation of helium by fast electron and proton impact

Abstract: We report the first experimental results on the state selective cross-section ratio a + */a* of helium for electron and proton impact. Our results show consistently higher yields for electrons than for protons at higher velocities. A comparison is made between the cross-section ratios

Cited by 35 publications

References 33 publications

Ionization–excitation of helium to He (2p) magnetic sublevels following electron, proton, and molecular hydrogen (H2 and H3 ) impact

Ionization–excitation of helium to He (2p) magnetic sublevels following electron, proton, and molecular hydrogen (H2 and H3 ) impact

Polarization measurements of the extreme ultraviolet (EUV) emission following excitation and ionization-excitation of helium by fast electron, proton, and molecular hydrogen (H 2 + and H 3 +) impact

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Abstract: We report the first experimental results on the state selective cross-section ratio a + /a of helium for electron and proton impact. Our results show consistently higher yields for electrons than for protons at higher velocities. A comparison is made between the cross-section ratios

Ionization–excitation of helium to He(2p) magnetic sublevels following electron, proton, and molecular hydrogen (H₂and H₃) impact

Ionization–excitation of helium to He(2p) magnetic sublevels following electron, proton, and molecular hydrogen (H₂and H₃) impact