Review of advances in describing the 31D-state excitation of helium

1996 ◽  
Vol 74 (11-12) ◽  
pp. 906-913
Author(s):  
J. F. Williams ◽  
A. G. Mikosza ◽  
J. B. Wang
Keyword(s):  
Scattering Amplitudes ◽  
Partial Cross Section ◽  
Stokes Parameters ◽  
Impact Excitation ◽  
Electron Impact Excitation ◽  
Scattered Electron ◽  
Close Coupling ◽  
Natural Frame ◽  
Electron Photon

Recent advances in describing the electron impact excitation of the 31D state of helium are reported for an incident energy of 40 eV and scattering angles from 10° to 40°. Measurements of the Stokes parameters have been made using the polarized photon–photon and electron–photon coincidence techniques. The partial cross section σm for the magnetic sublevels in the collision frame indicate that the m = 0 excitation is favoured. For the above scattering kinematics the data are in agreement with convergent close coupling calculations. The deduced scattering amplitudes, in the natural frame, show that the m = 2 excitation becomes dominant at the larger angles. Progress is reported on the complete determination of the scattering amplitudes and their relative phases using the triple-coincident detection of the scattered electron with the two sequential cascading photons.

Excitation of Ne VIII by electron impact

1976 ◽  
Vol 54 (20) ◽  
pp. 2019-2023 ◽  
Author(s):  
W. L. van Wyngaarden ◽  
Ronald J. W. Henry
Keyword(s):  
Electron Impact ◽  
Born Approximation ◽  
Experimental Error ◽  
Rate Coefficient ◽  
Impact Excitation ◽  
Rate Coefficients ◽  
Electron Impact Excitation ◽  
Close Coupling ◽  
Coupling Approximation ◽  
Made In

Collision strengths for electron impact excitation of Ne VIII are calculated at 14, 18, and 30 Ry in a 5-state close coupling expansion and the unitarized Coulomb–Born approximation. To assess the importance of exchange and coupling beyond the 5 states, additional calculations are made at 18 Ry in 5-state and 8-state close coupling expansions without exchange. For the 2s–2p excitation, calculations below the 3s threshold at 10.0 Ry are made in a 2-state close coupling expansion at 1.6, 3.2, and 8.0 Ry. In most instances the close coupling method gives results which differ by 15% or less from those of the unitarized Coulomb–Born approximation and by 20–70% from the CBI (Coulomb–Born) results of Bely. Rate coefficients which are calculated from the results obtained in the close coupling approximation agree within experimental error with the experimental results of Kunze and Johnston and Haddad and McWhirter with the exception of the rate coefficient for the 2p → 3d excitation.

A measurement of the cross section for production of He + (2 S ) ions by electron impact excitation of ground state helium ions

1966 ◽  
Vol 290 (1420) ◽  
pp. 74-93 ◽  
Keyword(s):  
Plane Wave ◽  
Cross Section ◽  
Cross Sections ◽  
Absolute Magnitude ◽  
Impact Excitation ◽  
Electron Impact Excitation ◽  
Close Coupling ◽  
Born Cross Section ◽  
The Absolute ◽  
The Cross

A crossed beams method has been used to measure the cross section for the production of He + (2 S ) by electrons incident upon He + (1 S ) in the energy range from threshold to 750 eV. The cross section was measured in arbitrary units with an accuracy of ± 5 % and at the higher energies its energy dependence is in close agreement with that calculated by means of the plane-wave Born approximation. Consequently the cross section has been normalized to the plane-wave Born cross section at energies between 435 and 750 eV to obtain the absolute magnitude. An independent estimate of the absolute magnitude was made to with in ± 30 % using only the experimental parameters, and the absolute cross sections given by the two methods agree within the experimental uncertainties. The normalized cross section is compared with cross sections given by the close-coupling approximation and various Coulomb-Born approximations. At the lower energies the normalized cross section is considerably smaller than any of the theoretical values, but the measurements are consistent with the existence of a finite cross section at threshold if the energy spread of the electron beam is taken in to account.

scholarly journals Effective collision strengths for electron-impact excitation of Al10+

2006 ◽  
Vol 24 (2) ◽  
pp. 235-240 ◽  
Author(s):  
V. STANCALIE ◽  
V. PAIS
Keyword(s):  
Electron Impact ◽  
Maximum Energy ◽  
Impact Excitation ◽  
Electron Collision ◽  
Electron Impact Excitation ◽  
Coupling Scheme ◽  
Close Coupling ◽  
R Matrix ◽  
Intermediate Coupling Scheme ◽  
Effective Collision

Electron collision strengths for electron-impact excitation of Li-like and Al ion are evaluated in close-coupling approximation using the multi-channel R-matrix method. Five LS target eigenstates are included in the expansion of the total wave function, consisting of the twon= 2 states withconfigurationsof 1s22s, 1s22p, and threen= 3 states withconfigurations1s23s, 1s23p, and 1s23d. Collision strengths are obtained in LS coupling using FARM code and in intermediate coupling scheme using the SUPERSTRUCTURE program. The effective collision strengths are calculated as function of temperature, up to a temperature that does not exceed half of the maximum energy in the R-matrix run.

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