Excitation of helium by 0.05–6 keV electrons and polarization of the resulting radiation

The polarisation fractions of radiation emitted following electron impact excitation of the n'P ( n = 2-6) and n'D ( n =3-6) states of helium have been calculated using first-order many-body theory over the energy range from threshold to 500 eV. The predicted polarisation fractions are essentially independent of the principal quantum number ( n ) , in agreement with the experimental results of Standage for n ' P ( n = 2,3) and the Born results of Vriens and Carriere, but in apparent disagreement with the multichannel eikonal results.

Section: Moustafa Energysupporting

confidence: 61%

“…Experimental results of Heddle and Lucas (1963) (not corrected for cascade). Experimental results of Moustafa Moussa et al (1969).…”

Section: Polarisation Fractions Following N ' ~ Excitationmentioning

confidence: 99%

Principal quantum number dependence of polarisation fractions for electron impact excitation of the n¹P and n¹D states of helium

Csanak¹,

Cartwright²

1989

“…It should be emphasized that both the metastable and ground-state cross sections used in equation ( 7) are apparent cross sections, that is, they represent the sum of direct excitation and cascade from all higher levels. A number of experimental measurements have been made for electron excitation of the ground state (1 1 S) of He into higher triplet levels, including the works of St John et al (1964), Jobe and St John (1967), Moustafa Moussa et al (1969), van Raan et al (1971,1974), and Showalter and Kay (1975). However, cross section measurements for excitation into levels with n > 5 are generally not available.…”

Section: Methodsmentioning

confidence: 99%

Electron excitation out of the metastable level of He into high-ntriplet levels

Piech

Chilton

Anderson

et al. 1998

“…Fursa and Bray (1995) have reported CCC results at selected energies and Bartschat (1998) has used the RMPS method for energies up to 40 eV. Absolute experimental emission cross sections have been determined by St John et al (1964) from threshold to 450 eV, Moustafa Moussa et al (1969) from 80 to 2000 eV, and Showalter and Kay (1975) from 50 to 500 eV. These have been complemented by the work of Anderson et al (1969) and Kay and Simpson (1988), who used time resolved spectroscopic techniques to obtain more realistic estimates of cascades and hence direct electron excitation cross sections for the 3 3 D state.…”

Section: Introductionmentioning

confidence: 99%

“…Relative emission cross sections and polarizations (uncorrected for cascades) have been measured from threshold up to 24.6 eV in a high-resolution experiment ( E 1/2 ≈ 0.040 eV) by Heddle et al (1974Heddle et al ( , 1977. Moustafa Moussa et al (1969) also measured polarization fractions for the 3 3 D → 2 3 P line from 80-1000 eV while Defrance (1980) and Batelaan et al (1991) reported polarization data in the region of doubly excited resonance states, He − (2s 2 2p) 2 P at 57.22 eV and (2s2p 2 ) 2 D at 58.30 eV.…”

Section: Introductionmentioning

confidence: 99%

Excitation and polarization of the 3³D state of helium by electron impact

Cvejanović¹,

Clague²,

Fursa³

et al. 2000

Electron impact excitation of the 33D state of helium has been studied experimentally and theoretically using the convergent close coupling (CCC) and R-matrix with pseudo-states (RMPS) methods. Experimental and theoretical CCC emission cross sections and polarizations of the 33D→23P line are reported. Theoretical cross sections for direct excitation of the 33D state and polarizations of corresponding emitted radiation are also reported using both CCC and RMPS methods. Particular attention has been given to making realistic estimates of the large cascade contributions to both the cross sections and the polarization fraction of the 33D→23P radiation, using the CCC approach. The self-consistency of the experimental and theoretical polarization data gives confidence in their quality. On the other hand differences remain between experimental and theoretical emission cross sections at higher energies.