Investigation of electron impact double excitation of the

Investigation of electron impact double excitation of the

Investigation of electron impact double excitation of the autoionizing states of
Helium by (e, 2e) experiments
Melike Ulu*1, Omer Sise§, Ali Alpergun*, Nurcin Karadeniz*, Mevlut Dogan* and Albert Crowe†
*
§
Department of Physics, e-COL Laboratory, Afyon Kocatepe University, Afyon, Turkey
Department of Science Education, Faculty of Education, Suleyman Demirel University, Isparta, Turkey
†
School of Chemistry, Newcastle University, Newcastle, United Kingdom
Synopsis We present experimental measurements of triple differential cross sections (TDCS) for the helium
autoionizing resonance states. Triple differential cross-sections can be obtained by measuring the energy and angular distributions of outgoing electrons by use traditional electron spectrometer.
Autoionization in atomic collisions is a
fundamental process that has attracted a lot of
interest for several decades since Madden and
Codling conducted their pioneering work on
helium in this field [1].
Autoionizing states are degenerate with
continuum (final ion plus ejected electron)
states from the direct ionization process. The
dynamics of this process can be uniquely
determined by (e, 2e) experiments in which
both the outgoing electrons resulting from the
same ionization event are detected in time
coincidence.
The (e, 2e) technique investigates electron
impact ionization provides the most detailed
insight into the reaction of many-body systems.
However, due to the low cross sections and
difficulties in achieving the required energy
resolution, the experimental investigations of
the double excitations of helium by this
technique are very limited. In two (e,2e) papers
[2,3], our group has published on He 2l2l’
autoionizing states for incident electron energy
of 250 eV at coplanar geometry. These works
1
e-mail: [email protected]
show that the resonance contributions together
with the strong background of direct ionization
processes lead to a complicated asymmetric
structure of the resonance profile in the TDCS.
In the conference, we will present recent measurements of the triple differential cross sections for
autoionizing states of helium in the 2l2l’ resonances.
Acknowledgments
This work was supported by the Scientific
and Technological Research Council of Turkey
(TUBITAK) through grant 109T738 and AKUBAPK through grant 14.FENED.05.
References
[1] R. P. Madden and K. Codling 1965 Astrophys. J.
141, 364.
[2] O. Sise, M. Dogan, I. Okur, A. Crowe 2010 J.
Phys. B: At. Mol. Op. Phys. 43 185201.
[3] O. Sise, M. Dogan, I. Okur, A. Crowe 2011
Phys. Rev. A 84 (2) 022705.