Abstracts from Journal of Physics:B-Atomic Molecular Optical Physics
Relative Differential
cross sections for the electron Impact Excitation of the 33P, 31D and 33D states
of Helium
H Batelaan, F Vercoulen, J van Eck and H G M Heideman
Buys Ballotlab., Utrecht Rijksuniv., Netherlands
Abstract The authors present measurements
of relative differential cross sections for the electron impact excitation of
the 31D, 33D and 33P states of helium at energies of 40, 45, 60 and 80 eV and
for scattering angles ranging from 30' to 120'. The results are extracted from
existing data of electron-photon coincidence experiments. The results are in
agreement with distorted wave calculations. The authors point out the consistency
of the results with the angular behaviour of the coherence parameter rho 00
also obtained from these coincidence experiments.
J. Phys. B: At. Mol. Opt. Phys. 24 (28 August 1991)
L397-L403
In-plane coincident
measurements on the Excitation of the 31D and 33D states of Helium by Electron
impact
H Batelaan, J van Eck and H G M Heideman
Buys Ballotlab., Rijksuniv. Utrecht, Netherlands
Abstract The authors have studied
the excitation of the 31D and the 33D state of helium by electron impact. They
measured the linear polarization of the decay radiation emitted in the scattering
plane using the well known polarization correlation technique. Combining these
results with previous measurements (also from other research groups) yields
the parameters, which describe the dynamics and shape of the excited states.
J. Phys. B: At. Mol. Opt. Phys. 23 (14 November 1990)
3993-4004
Electron Impact Excitation
of the 33P state of Helium: Coherence Parameters
H Batelaan, J van Eck and H G M Heideman
Buys Ballot Lab., Rijksuniv. Utrecht, Netherlands
Abstract In an electron-photon
coincidence experiment the authors have measured the polarization degree of
the decay radiation from the electron impact excited 33P to 23S transition in
helium. They performed their measurements perpendicular to the scattering plane.
To analyse the polarization they used a beam splitting polarizer instead of
the usual sheet polarizer. The linear polarization degree was measured at an
electron impact energy of 40 eV and the circular polarization degree was measured
at 40, 60 and 80 eV. The electron scattering angle ranged from 32.8' to 116'.
The experimentally determined degrees of polarization are in good agreement
with the theoretical results of the distorted-wave Born approximation (DWBA).
The scaling relation of Lin et al. (1989) is in agreement with the DWBA results
of the circular polarization for 33P excitation.
J. Phys. B: At. Mol. Opt. Phys. 21 (28 December 1988)
L741-L745
Measurement of Coherence
Parameters for the electron impact excitation of the 31D state of Helium at
small electron scattering angles
H Batelaan, J van Eck and H G M Heideman
Buys Ballotlab., Rijksuniv. Utrecht, Netherlands
Abstract The authors have measured
the Stokes parameters of the coincident decay radiation resulting from the electron
impact excitation of the 31D states of helium. This was done as a function of
the electron scattering angle theta e in the small scattering angle range (15'-30')
at energies of 45 and 60 eV. The results do not provide a preference for any
of the theoretical models currently available. Measurements of the Stokes parameter
P3 (proportional to Lperpendicular to ) tend to confirm the predictions of the
distorted-wave Born approximation (DWBA). For the coherence parameters Pl and
gamma resulting from the measurements of P1 and P2, the results for Pl seem
to be consistent with the dipole multichannel eikonal treatment (DMET) and with
the first-order many-body theory (FOMBT), whereas the results for gamma are
in disagreement with these theories.
J. Phys. B: At. Mol. Opt. Phys. 24 (28 December 1991)
5151-5167
The influence of Negative ion resonances
on the electron impact excitation of the 33D state of Helium near 60 eV
H Batelaan, J van Eck and H G M Heideman
Buys Ballotlab., Rijksuniversiteit Utrecht, Netherlands
Abstract The authors have studied
the electron impact excitation of the 33D state of helium at incident energies
near the well known negative ion resonances He-(2s2 2p) 2P and He-(2s2p2) 2D
at 57.2 and 58.3 eV respectively. This was done by measuring the polarization
degree of the radiation emitted in the subsequent 33D to 23P transition both
in a non-coincidence and a coincidence experiment. As the direct excitation
process of 33D and the indirect excitation process via a negative ion resonance
are indistinguishable, these processes interfere. Analysis of the present and
previous results indicate that the effects of interference play a minor role
for the polarization degree as measured in the non-coincidence experiment. For
the coincidence experiment the effects of interference are important.