Faculté des sciences

Low-lying resonances in electron-argon scattering: Measurements at 5-meV resolution and comparison with theory

Franz, K. ; Hoffmann, T. H. ; Bömmels, J. ; Gopalan, A. ; Sauter, G. ; Meyer, W. ; Allan, Michael ; Ruf, M.-W. ; Hotop, H.

In: Physical Review A, 2008, vol. 78, no. 1, p. 012712

Combining a laser photoelectron source with a triply differentially pumped supersonic beam target and several electron multipliers for simultaneous detection of electrons elastically scattered into the angles 22.5°, 45°, 90°, 112.5°, and 135° and of metastable atoms due to inelastic scattering, we have carried out an improved study of electron-argon scattering over the energy range... Plus

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    Summary
    Combining a laser photoelectron source with a triply differentially pumped supersonic beam target and several electron multipliers for simultaneous detection of electrons elastically scattered into the angles 22.5°, 45°, 90°, 112.5°, and 135° and of metastable atoms due to inelastic scattering, we have carried out an improved study of electron-argon scattering over the energy range 11.0–13.7  eV with experimental energy widths around 5  meV. In addition, the Fribourg scattering apparatus has been used for careful remeasurements of the differential cross section and the resonance structure in the energy range of the two lowest anion resonances over the full angular range at a resolution of about 13  meV. Accurate values for the energies, the widths (2.3±0.2  meV), and the fine-structure separation (172.7±0.2  meV) of the low-lying Ar⁻(3p⁵4s²  ²P3/2,1/2) Feshbach resonances have been determined from the two experiments by detailed partial-wave analyses of the resonance profiles using several sets of energy-dependent background phase shifts; these include an accurate set obtained with a coupled-cluster calculation involving a soft box potential. Moreover, the excitation function for the production of metastable Ar*(3p⁵4s  ³P2,0) atoms has been measured from threshold to 13.7  eV. From a fit to its onset, the absolute electron energy scale is established to within ±0.3  meV; in addition, the energies and widths of some higher-lying resonances (12.9–13.5  eV) have been determined and are compared with the results of earlier experiments and of a recent B-spline R-matrix calculation. In connection with calibration experiments involving He atoms, we carried out an improved measurement of the He⁻(1s2s²  ²S1/2) resonance and deduced a natural width of 10.9±0.3  meV.