Quantum mechanically complete measurements in electron impact excitation of helium

Mikosza, Andrew G.
February 2000
AIP Conference Proceedings;2000, Vol. 500 Issue 1, p297
Academic Journal
A complete quantum description of the 3[sup 1]D state of helium, that is the amplitudes and relative phases for the m=0,±2 magnetic sublevels are reported. All state multipoles 〈T(2)kq〉 (k=0–4,k>=q>=-k) that describe the population and the anisotropy of the excited He(3[sup 1]D) state are presented. The data were determined for 60 eV incident electrons and 40° electron scattering angle. The experimental procedure was to measure the triple-coincidence, polarization correlations of the sequential cascading photons (667.8 nm 3[sup 1]D→2[sup 1]P and 58.4 nm 2[sup 1]P→1[sup 1]S transitions) and the scattered n=3 energy loss electrons. Simultaneous measurements of the three two-particle coincidence pairs determined accurate magnitudes of the scattering amplitudes and phases as well as enabling consistency checks with earlier data. The triple coincidence data determined the sign of the relative m=±2 phases. The results are presented in a simplifying diagrammatic form. As yet there are no other complete experimental determinations of the 3[sup 1]D state. The measurements are in agreement, within the experimental uncertainty, with the Convergent Close Coupling (CCC) calculations. Previous data for helium at 40 eV incident electrons are discussed in the context of the present triple-coincidence results. The desirability of a recently introduced parameter notation for the helium 3[sup 1,3]D states is questioned with respect to physical insight. © 2000 American Institute of Physics.


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