Spin-Dependent Orientation Propensities Revealed in Polarized-Electron–Polarized-Photon Coincidence Studies

Andersen, N.; Bartschat, Klaus; Jt, Broad; Gf, Hanne; Uhrig, Martin

doi:10.1103/physrevlett.76.208

Cited by 24 publications

(15 citation statements)

References 19 publications

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“…Extensive compilations [4] of the available experimental data at the time, and many more theoretical predictions, showed the propensity for a positive angular momentum transfer at small scattering angles in S → P excitation to be seemingly very well fulfilled for the case of unpolarized incident electrons. An important generalization was presented by Andersen et al [13], who analyzed the so-called generalized Stokes parameters [5,14] for a spin-polarized projectile beam. They found that parity conservation required the opposite sign of L ⊥ for spin-up and spin-down (relative to the scattering plane) electrons for forward scattering.…”

Section: Introductionmentioning

confidence: 99%

Polarization correlations for electron-impact excitation of the resonant transitions of Ne and Ar at low incident energies

et al. 2013

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The electron-polarized-photon coincidence method is used to determine linear and circular polarization correlations in the vacuum ultraviolet (VUV) for the differential electron impact excitation of neon and argon resonance transitions at impact energies of 25 eV and 30 eV at small scattering angles up to 40 o. The circular polarization correlation is found to be positive in the case of Ne at 25 eV and supports the prediction of the present B-spline R-matrix theory concerning the violation of a longestablished propensity rule regarding angular momentum transfer in electron impact excitation of S → P transitions. Comparisons with the results from the present Relativistic Distorted-Wave Approximation and an earlier Semi-Relativistic Distorted-Wave Born model are also made. For the case of Ar, at 25 eV and 30 eV, the circular polarization measurements remain in agreement with theory, but provide limited evidence to whether or not the circular polarization at small scattering angles is also positive. For the linear polarizations, much better agreement with theory is obtained than in earlier measurements carried out by Zheng and Becker (Z.

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Section: Introductionmentioning

confidence: 99%

Polarization correlations for electron-impact excitation of the resonant transitions of Ne and Ar at low incident energies

et al. 2013

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“…P o excitation, almost without exception (see Ref. [12] for a rare example), the value of L Ќ is positive for small scattering angles u and increases with u to a maximum beyond which the variation becomes more individual. (See Ref.…”

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confidence: 96%

Propensity Rules for Angular Momentum Transfer in Electron-Impact Excitation and Deexcitation

1999

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Following the recent investigation of Shurgalin et al. [Phys. Rev. Lett. 81, 4604 (1998)], electronimpact induced 3s ! 3p and 4s ! 3p transitions in atomic sodium are studied theoretically. A propensity rule for the angular momentum transfer is supported for scattering angles below 60 ± and incident energies below 20 eV. Excellent agreement between the predictions from an R matrix with pseudostates calculation and the experimental data is obtained and provides credibility to the present study.PACS numbers: 34.80.Dp Ever since the pioneering discussion by Kohmoto and Fano [1], a parameter of particular interest in the detailed study of atomic collisions has been the so-called "orientation" of the target, which describes the sense of circulation of the active electron(s) around the atomic core. This parameter can be studied in scattered-particlepolarized-photon coincidence experiments, in which the circular polarization P 3 of the light emitted perpendicular to the scattering plane is determined [2]. For the simplest case of 1 S ! 1 P o excitation without spin exchange and relativistic effects, P 3 , the orientation O 12 and the angular momentum transfer L Ќ are related through P 3 22O 12 2L Ќ . For more complicated situations, the result becomes P 3 2fL Ќ [2]. The factor f describes depolarization effects due to atomic fine structure and hyperfine structure, cascading if more than one photon can be emitted, and possibly relativistic effects.Alternatively, the angular momentum transfer can be studied in the "time-reversed" experiment, starting with a laser-prepared state. Following early work by Hertel et al. [3,4], this method was further developed by the NIST group [5-7] who generated benchmark data for 3s ! 3p electron-impact excitation in sodium. Subsequently, the technique was widely applied [8][9][10][11].Interestingly, the observed pattern for the angular momentum transfer as a function of the scattering angle showed a characteristic behavior, essentially independent of the collision energy and even the actual target. For electron-impact induced S ! P o excitation, almost without exception (see Ref.[12] for a rare example), the value of L Ќ is positive for small scattering angles u and increases with u to a maximum beyond which the variation becomes more individual. (See Ref. [13] for an extensive compilation of the available data.) Triggered by these results, considerable effort has been directed into finding a solid theoretical foundation for this empirical propensity rule, the Kohmoto-Fano paper being an early example. Propensity rules for orientation have also been formulated and discussed for heavy-particle impact excitation [14], and efforts have concentrated on exploring the generality of these rules [15,16].For electron-atom collisions, a significant step beyond the Kohmoto-Fano work was the analysis by Madison and Winters [17]. After pointing out a phase problem in the Kohmoto-Fano paper, they discussed the orientation parameter in terms of the charge q of the projectile, with q 61 for positron and...

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“…After tedious algebraic manipulations, we have also extracted spin-resolved alignment and orientation parameters from these data which lead to· interesting conclusions about the validity of propensity rules. The results will be presented elsewhere (Andersen et al 1996b). …”

Section: Example Resultsmentioning

confidence: 94%

“…For symmetry reasons, we prefer these weights over the parameter r = at / as that denotes the ratio of the triplet and the singlet cross sections. These parameters are related as follows (for details see Andersen et al 1996b):…”

Section: Spin-resolved Alignment and Orientation Effects Ao')mentioning

confidence: 99%

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Spin-resolved Alignment and Orientation Effects in Atomic Collisions

Bartschat¹,

Andersen²

1996

Aust. J. Phys.

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The density matrix parametrisation of collisionally excited atomic ensembles is generalised to account for projectile and target spin polarisations. The density matrix elements, containing spin-resolved alignment and orientation parameters, can be determined by measurements of the 'generalised Stokes parameters' introduced by Andersen and Bartschat (1994) to describe scattered-projectile-polarised-photon coincidence experiments. Focusing on electron impact excitation of light alkali-type targets and mercury, the present experimental status of such experiments is reviewed, in particular with regard to the 'perfect scattering experiment' whereby all independent scattering amplitudes are determined.

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Spin-Dependent Orientation Propensities Revealed in Polarized-Electron–Polarized-Photon Coincidence Studies

Cited by 24 publications

References 19 publications

Polarization correlations for electron-impact excitation of the resonant transitions of Ne and Ar at low incident energies

Polarization correlations for electron-impact excitation of the resonant transitions of Ne and Ar at low incident energies

Propensity Rules for Angular Momentum Transfer in Electron-Impact Excitation and Deexcitation

Spin-resolved Alignment and Orientation Effects in Atomic Collisions

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