Excitation of autoionizing states of helium by 100 keV proton impact: theory and experiment

Godunov, Alexander; Schipakov, V A; Moretto-Capelle, P; Bordenave-Montesquieu, D; Benhenni, Malika; Bordenave-Montesquieu, A

doi:10.1088/0953-4075/30/23/012

Cited by 25 publications

(70 citation statements)

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“…Therefore, comparing the calculation results for two-electron excitation with available experimental data (electron spectra or resonance parameters) requires not only an adequate theoretical description of the double excitation itself, but also a realistic description of the direct ionization, including the interference of resonant and direct ionization. Moreover, Coulomb interaction in the final state (CIFS) between the scattered charged particle, the ejected electron, and the recoil ion considerably influences the resonance profiles [5][6][7][8]. Under the conditions of strong CIFS the shapes of the resonant lines can be very different from the familiar Fano's one [5,7] complicating the comparison of experimental and theoretical results, and hence the description of three-body Coulomb interaction of charged particles must be as accurate as the description of twoelectron excitation [8].…”

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confidence: 99%

“…Moreover, Coulomb interaction in the final state (CIFS) between the scattered charged particle, the ejected electron, and the recoil ion considerably influences the resonance profiles [5][6][7][8]. Under the conditions of strong CIFS the shapes of the resonant lines can be very different from the familiar Fano's one [5,7] complicating the comparison of experimental and theoretical results, and hence the description of three-body Coulomb interaction of charged particles must be as accurate as the description of twoelectron excitation [8]. The theoretical excitation cross sections reported in this paper are part of our complete calculation [8] where all these problems are solved.…”

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First Double Excitation Cross Sections of Helium Measured for 100-keV Proton Impact

Moretto-Capelle

Bordenave-Montesquieu

et al. 1997

Phys. Rev. Lett.

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Excitation cross sections of the ͑2s 2 ͒ 1 S, ͑2p 2 ͒ 1 D, and ͑2s2p͒ 1 P autoionizing states of helium, produced in collisions with 100-keV protons, have been measured for the first time. Using a high resolution electron spectroscopy together with a recently proposed parametrization of autoionizing resonances distorted by Coulomb interaction in the final state makes it possible to extract from electron spectra total cross sections as well as magnetic sublevel populations. These new experimental data are briefly compared with out theoretical calculations. [S0031-9007 (97)04892-8] PACS numbers: 34.50.FaTwo-electron excitation of the helium atom by proton impact is currently a benchmark test for the theories of multielectron transitions which try to understand the excitation mechanisms involved in heavy particle collisions [1]. Doubly excited states of helium lie above the singleionization threshold and decay primarily by autoionization. Since the excitation and subsequent nonradiative decay of autoionizing states is coherent with direct ionization, the resonant and direct ionization amplitudes should be added together, rather than cross sections of both processes [2]. This results in at least two effects. First, the resonances in ionization cross sections are asymmetric. They are commonly described by Fano's formula [2]. Second, the intensity of an autoionizing resonance is not proportional to the population of the resonant state [3]. The total resonant yield can provide only a lower estimate for the excitation cross section at asymptotic collision velocities [4]. This means that information on two-electron excitation is hidden in the resonance profiles. Therefore, comparing the calculation results for two-electron excitation with available experimental data (electron spectra or resonance parameters) requires not only an adequate theoretical description of the double excitation itself, but also a realistic description of the direct ionization, including the interference of resonant and direct ionization. Moreover, Coulomb interaction in the final state (CIFS) between the scattered charged particle, the ejected electron, and the recoil ion considerably influences the resonance profiles [5][6][7][8]. Under the conditions of strong CIFS the shapes of the resonant lines can be very different from the familiar Fano's one [5,7] complicating the comparison of experimental and theoretical results, and hence the description of three-body Coulomb interaction of charged particles must be as accurate as the description of twoelectron excitation [8]. The theoretical excitation cross sections reported in this paper are part of our complete calculation [8] where all these problems are solved. From another point of view, if we are able to extract excitation cross sections from experimental data instead of resonance yields a comparison with less complex calculations becomes also possible. Indeed, several approximate theoretical models [9][10][11][12][13] have been developed in the past to discuss the excitation mechanisms; they ca...

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confidence: 99%

mentioning

confidence: 99%

First Double Excitation Cross Sections of Helium Measured for 100-keV Proton Impact

Moretto-Capelle

Bordenave-Montesquieu

et al. 1997

Phys. Rev. Lett.

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“…The role of the three-body Coulomb interaction in the ¢nal state between the ejected electron, the scattered proton, and the recoil helium ion is emphasized. 165 Mutual neutralization rates for H 3 O (H 2 O) n 0^3 OH À (H 2 O) m 0^3 have been determined using a new type of apparatus providing electrostatically merged ion beams. A pronounced enhancement of the rate is observed with clustering, which is interpreted as a change from electron transfer at small cluster size to proton transfer with more clustering.…”

Section: Gasesmentioning

confidence: 99%

7 Radiation chemistry

Belloni

Delcourt

Houée-Levin⊥

et al. 2000

Annu. Rep. Prog. Chem., Sect. C

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We try in this review to survey advances in all the aspects of Radiation Chemistry (the effects of high energy or ionizing radiation), both basic and applied, made during the period 1995^1999, after the last report issued at the end of 1994. 1 Classically, two main classes of studies are relevant. The ¢rst one includes the primary phenomena induced by the interaction of high-energy radiation with a chemical system. The way the energy is spatially deposited is indeed highly nonhomogeneous and depends on the type of radiation considered. Mutual reactions between the primary species produced also depend on their initial spatial distribution, and therefore on the energy absorption pattern. The kinetic aspects derive directly from the initial events following radiation absorption and thus, when observed at times as short as possible, give useful information on the early energy distribution for each of the radiation types, X-and g-photons, electrons and heavy particles, and, on the in£uence of their intensity and energy per particle.The second class of studies utilizes the background knowledge of radiation chemistry to generate and then to observe the fate of chemical transient species known to be involved in very important chemical or biochemical processes. Numerous data, such as the nature of reaction products, the absolute rate constants, the sequence of elementary reactions constituting a mechanism, and the thermodynamic and spectroscopic properties of short-lived species have been attained. This kind of study of transients and reaction mechanisms, which can be approached only by pulse techniques (essentially pulse radiolysis or laser photolysis, each with its speci¢c advantages), constitutes the new ¢eld of fast to ultrafast chemistry. It concerns extended domains of physical, organic, inorganic, and bio-chemistry. Moreover, the understanding of mechanisms is quite helpful in suggesting new ways of synthesis or degradation induced by irradiation and is now extensively used in developing various speci¢c processes in applied chemistry. The number of studies on the chemical mechanisms and in applied radiation chemistry constitutes an increased fraction of the total publications in radiation chemistry, which we estimate to be around 4000 over the period considered (almost constant compared to the preceding 5-year

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“…Under these conditions information about the population of the doubly excited states can be obtained by the analysis of the energy spectra of the ejected electron, the dierent autoionizing states appearing as resonances. The theoretical interpretation of these experimental spectra is dicult, because of the interference of the direct and resonant ionization processes, and the three-body Coulomb interaction in the ®nal state between the scattered projectile, ejected electron and the residual ion [29].…”

Section: Introductionmentioning

confidence: 99%

“…Very recently, the complete theoretical description of the resonant ionization processes at intermediate projectile energies (100 keV/amu) performed by Godunov et al [29] made possible for Moretto-Capelle et al [37] to extract double excitation cross sections from their experimental spectra of the ejected electron, obtained with a high-resolution spectrometer. These cross sections not only complete the experimental data of Giese et al [36] to lower energies, but are stated to be more exact, making sense for the comparison of dierent theoretical results with the experiment.…”

Section: Introductionmentioning

confidence: 99%

Multi-electron processes in atomic collisions – theory

Nagy

1999

Nuclear Instruments and Methods in Physics Research Section B:

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For the theoretical description of the multi-electron processes induced by charged particle impact we use a relatively simple perturbative method. The second-order approximation is valid for protons and antiprotons of moderate and high velocities. Electron correlation is taken into account by the use of con®guration-interaction wavefunctions. The agreement with the available experimental data for some two-electron processes in the helium depends on the quality of the wavefunctions used. Ó

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Excitation of autoionizing states of helium by 100 keV proton impact: theory and experiment

Cited by 25 publications

References 52 publications

First Double Excitation Cross Sections of Helium Measured for 100-keV Proton Impact

First Double Excitation Cross Sections of Helium Measured for 100-keV Proton Impact

7 Radiation chemistry

Multi-electron processes in atomic collisions – theory

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