Superelastic electron scattering on lithium

Karaganov, V.; Bray, Igor; Teubner, P. J. O.; Farrell, Peter M.

doi:10.1103/physreva.54.r9

Cited by 26 publications

(16 citation statements)

References 10 publications

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“…The discrepancy with experiment here undermines the basic building blocks of such theories. For this reason it is imperative that this problem be resolved as soon as possible" [1]. This quote is typical of a number made by various authors in recent years and it would be difficult for the present authors to put the present experimental study more vividly in context.…”

Section: S-2p Excitation Of Atomic Hydrogen By Electron Impact Studimentioning

confidence: 90%

1s-2p Excitation of Atomic Hydrogen by Electron Impact Studied Using the Angular Correlation Technique

1997

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Excitation of the 2p state of atomic hydrogen by electron impact was studied using the electronphoton angular correlation technique with the aim of resolving a long-standing and serious discrepancy between theories and previous experiments at large scattering angles. At a scattering angle of 100 ± , where the discrepancy was greatest, the present result shows excellent agreement with the theoretically predicted correlations. [S0031-9007(97)04312-3] PACS numbers: 34.80.Dp "There has been a very long-standing discrepancy at large scattering angles between theory and measurements of the 2 2 P angular correlation parameters for 54.4 eV electron-impact excitation of atomic hydrogen. In our view, this is the most outstanding problem in fundamental electron-atom scattering. The development of most electron-atom scattering theories use the e-H system as a testing ground for dealing with the more sophisticated problems. The discrepancy with experiment here undermines the basic building blocks of such theories. For this reason it is imperative that this problem be resolved as soon as possible" [1]. This quote is typical of a number made by various authors in recent years and it would be difficult for the present authors to put the present experimental study more vividly in context.Study of electron impact excitation processes using either the electron-photon angular correlation method, in which the angular distribution of the decay photon is measured in coincidence with the electron scattered in a particular direction, or the electron-photon polarization correlation method, where the polarization state of the emitted radiation is determined for a specific scattered electron momentum, is now well established [2]. In principle correlation methods can provide a complete quantum mechanical description of excitation processes. In practice this is true for only a limited number of cases, for example, S -P excitation in helium. Spin averaged correlation studies, such as those reported here, for S -P excitation in hydrogen are incomplete because the different spin channels can be resolved using spin polarized beams. Nevertheless these measurements provide the most stringent test of theoretical models for excitation of hydrogen presently available.Experimentally, correlation measurements for hydrogen have been hampered by the difficulties of producing suitable beams of hydrogen atoms, stable over a long period of time and by the depolarization of the radiation due to fine structure. Only three independent experimental research groups have made correlation measurements for the ͑1S -1P͒ excitation process [3][4][5][6][7][8][9][10]. Of these only the data of Weigold et al. [5] and Williams [6,7] have been made over a wide range of electron scattering angles at an incident electron energy of 54.4 eV. There is accord between these two sets of data at all scattering angles but because of the large statistical uncertainties in the data of Weigold et al. [5] further discussion of that work is not given here. Conversely this excitation proc...

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Section: S-2p Excitation Of Atomic Hydrogen By Electron Impact Studimentioning

confidence: 90%

1s-2p Excitation of Atomic Hydrogen by Electron Impact Studied Using the Angular Correlation Technique

1997

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“…Further, the line strength of these transitions enables efficient excitation of atoms to the P-state. Subsequent to the studies on sodium, the Flinders group has published data for lithium and potassium (Karaganov et al 1996, Stockman et al 1998. Excellent agreement with CCC calculations was again achieved.…”

Section: Introductionmentioning

confidence: 90%

Superelastic electron scattering from laser excited rubidium at 20 eV incident energy

Hall¹,

Shen²,

Murray³

et al. 2004

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

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Superelastic electron scattering measurements are presented from rubidium atoms excited by laser radiation to the 5 2 P states at around 780 nm. The incident energy of the electrons was 18.4 eV corresponding to 20 eV incident electrons for the excitation process 5 2 S-5 2 P. The measurements were conducted over a range of scattering angles from 5 • through to 125 •. A complete set of atomic collision parameters for the interaction process is presented together with the associated pseudo-Stokes parameters obtained from the measurements. A comparison with three sophisticated theoretical models indicates that none of the models completely describes the interaction process at this energy, and that further experimental and theoretical work is needed.

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“…At both 25 • and 30 • , the deviation is mostly caused by the measured P 3 , which significantly deviates from the theoretical prediction. The significance of these low values of P + is not clear as the source of the discrepancy for P 3 is not yet understood.…”

Section: Sourcementioning

confidence: 96%

Direct measurement ofP⁺for electron impact excitation of H(2p) at 54.4 eV

Grądziel¹,

O'Neill²

2004

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

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We report results of direct measurements of the reduced Stokes parameters P 1 ,P 2 andP 3 for electron impact excitation of H(2p) at 54.4 eV over the scattering range 10-40 •. These three parameters have been measured simultaneously for the first time using a VUV double-rotation polarization analyser consisting of a MgF 2 retarder followed by a SiO 2 reflection linear polarizer. As expected, our measurements forP 1 andP 2 are in good agreement with theoretical calculations and previous experimental data. Our data forP 3 differ significantly from previous experimental measurements and theoretical calculations. Consequently, we find that the coherence parameter P + deviates significantly from unity at 30 •. If correct, this signifies that spin-exchange scattering may be more important than has previously been thought.

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Superelastic electron scattering on lithium

Cited by 26 publications

References 10 publications

1s-2p Excitation of Atomic Hydrogen by Electron Impact Studied Using the Angular Correlation Technique

1s-2p Excitation of Atomic Hydrogen by Electron Impact Studied Using the Angular Correlation Technique

Superelastic electron scattering from laser excited rubidium at 20 eV incident energy

Direct measurement ofP⁺for electron impact excitation of H(2p) at 54.4 eV

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Superelastic electron scattering on lithium

Cited by 26 publications

References 10 publications

1s-2p Excitation of Atomic Hydrogen by Electron Impact Studied Using the Angular Correlation Technique

1s-2p Excitation of Atomic Hydrogen by Electron Impact Studied Using the Angular Correlation Technique

Superelastic electron scattering from laser excited rubidium at 20 eV incident energy

Direct measurement ofP+for electron impact excitation of H(2p) at 54.4 eV

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Direct measurement ofP⁺for electron impact excitation of H(2p) at 54.4 eV