Quantum mechanically complete measurements in electron impact excitation of helium

Abstract

A complete quantum description of the 3 ! 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 1 D) state are presented. The data were determined for 60eV incident electrons and 40°e lectron scattering angle. The experimental procedure was to measure the triple-coincidence, polarisation correlations of the sequential cascading photons (667.8 nm 3 ] D->2'P and 58.4 nm 2 1 P-»1 1 S transitions) and the scattered n = 3 energy loss electrons. Simultaneous measurements of the three twoparticle 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 ! D state. The measurements are in agreement, within the experimental uncertainty, with the Convergent Close Coupling (CCC) calculations. Previous data for helium at 40eV 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 1)3 D states is questioned with respect to physical insight.

Angular Momentum Partitioning and Hexacontatetrapole Moments in Impulsively Excited Argon Ions

“…There have been several other studies of collisionally produced hexadecapole moments in atoms [16,17], and three groups have used Stokes parameter measurements to study ionization/excitation collisions in the heavy noble gases [4,[18][19][20]. To our knowledge, the present work represents the first study of angular momentum partitioning between shells of an excited state and the measurement of an atomic hexacontatetrapole.…”