Investigation of electron impact double excitation of the
Transkript
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: mzekiler@aku.edu.tr 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.