XXVII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2011) IOP Publishing Journal of Physics: Conference Series 388 (2012) 102030 doi:10.1088/1742-6596/388/10/102030
Transfer ionization in swift D+ on H2 collisions dependence of the electron emission on the internuclear distance Markus Waitz* 1, Florian Trinter*, Christian Müller*, Christoph Goihl*, Annika Jung*, Hong-Keun Kim*, Jasmin Titze*, Markus S. Schöffler†, Till Jahnke*, Achim Czasch*, Lothar Ph. H. Schmidt*, Horst Schmidt-Böcking* and Reinhard Dörner* 2 *
Institut für Kernphysik, Goethe Universität Frankfurt, Max-von-Laue-Str. 1, D-60438 Frankfurt am Main, Germany † Institut für Photonik, Technische Universität Wien, Gusshausstr. 27-29, A-1040 Wien, Austria Synopsis In highly differential transfer ionization measurements with atomic targets the binary encounter and the shake off process can be distinguished by means of the electron longitudinal momentum. We observe a similar dependency for the case of a molecular target. In addition, a surprising dependence of electron emission on the internuclear distance is found.
Transfer ionization in swift (several a.u. velocity) ion Helium collisions leads to a rich structure in the momentum distribution of the emitted electron ([1], [2], [3]). One part of the electrons is emitted in the forward direction, similar to single ionization. There is however also a strong distinct peak of backward emitted electrons. The origin of this structure is still under dispute. The forward emitted electrons might be associated with a two step process, where two independent interactions of the projectile with either electron leads to capture of one and ionization of the second one. The second mechanism contributing to transfer ionization is single capture accompanied by a shake off of the second electron. One hypothesis, backed by calculations ([4]), is that the backward electrons are caused by initial state correlation and the shake off process. According to this argument one of the two electrons is captured into the forward direction and by initial state correlation the second electron is than more likely to be shaken off to the backward direction. Here we report on the first experimental observation of transfer ionization on molecular hydrogen. We find a surprising dependence of electron emission on the internuclear distance. For our investigation we used 150 keV/u D+ projectiles from a Van-de-Graaff accelerator. The measured reaction channel is the following: D+ + H2 -> D0 + H+ + H+ + e1
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1
Using the COLTRIMS (COLd Target Recoil Ion Momentum Spectroscopy) imaging technique, the three dimensional momentum vector of every charged particle is measured. The H2 target molecules are prepared in a supersonic gas jet. After the reaction electric and magnetic fields project and guide the charged particles onto time and position sensitive detectors. The results of our measurement can be compared to the case of an atomic target: The momentum distribution of the measured electron shows a clear sub-division into forward and backward emission of the electron. In addition, a molecule specific effect was observed. The forward part of the electron momentum distribution gives higher values for perpendicular orientation of the molecule with respect to the incident beam direction. The SO part does not show this dependence. As a result, the ratio between forward and backward emission changes with internuclear distance. References [1] Europhys. Lett., 62 (4), p. 477-483 (2003) [2] J. Phys. B: At. Mol. Opt. Phys. 38 (2005), L123L128 [3] Phys. Rev. Lett. 86 (2001) 2257 [4] Phys. Rev. A 71, 052712 (2005)
