Excitation of He(31 D) by electron impact

Abstract

Abstract.We report new results of the Stokes parameters P1 to P4 and of the coherence parameters Plin, Ya, P0o and L± for He(3 ~D) excitation by electron impact in the energy range 40 eV to 81.6 eV obtained by the scattered electron-polarized photon coincidence technique. The present results are, where available, in fair agreement with previous measurements of other groups but disagree with the available calculations based on different models.

Quantum mechanically complete measurements in electron impact excitation of helium

“…The right hand side columns show the alternative phases j3 +2 °r ft+2 > an d P-l or P-2 » f°r me a +2 an d oc_ 2 amplitudes, respectively. The values of P i ( i = 1, 2, 3 and 4) agree well with our previous polarization correlations experiments (13).…”

“…More detailed measurements included the determination of Stokes parameter P 4 by measurements in-the-scattering plane of polarisation correlations and hence the electron charge cloud height parameter p 00 (12)(13)(14).…”

Complete Determination of Excitation Amplitudes and Phases for the31DState of Helium

“…Figure 3 indicates our earlier [9] twoparticle ͑e 2 , g 1 ͒ coincidence measurements at electron scattering angles of 15 ± and 25 ± from which pairs of phases are obtained; however, there the experimental uncertainties are clearly too large for separation of the phase pairs. Nevertheless, it is noted that, having identified the true phase pair from triple-coincidence limits, that is, the real inversion symmetry of the phases, the values shown by inverted triangles would be expected to be real phases.…”

“…For the 3 1 D state of helium studied here, the polarization requires specification of only an axis of symmetry and has been measured frequently since about 1964 [6]. However, angular and polarization correlation analyses, requiring a plane of symmetry and hence the detection of two outgoing particles (the scattered energy loss electron and either the 3 1 D to 2 1 P or 2 1 P to 1 1 S photon), have been made only since about 1987 [7][8][9][10]. Similar measurements of the correlations of the two sequential cascading photons, but without the detection of the scattered electron [11], determine only the amplitudes squared, that is the partial cross sections for the magnetic substates.…”

“…The relative phases b 12 and b 22, of the amplitudes a 12 and a 22 , respectively, as a function of the electron scattering angle. The two-particle ͑e 2 , g 1 ͒ coincidence measurements provide the possible real b II ͑=͒ and ghost b I ͑D͒[9] values. At 40 ± scattering angle, the double coincidence data, obtained concurrently with triple coincidence measurements, are identified as the real b II ͑͒ and as the ghost b I ͑}͒ solutions.…”