Kinematisch vollständige und zustands-selektive Untersuchung der stoßinduzierten Einfachionisation von Lithium

Die Untersuchung stoßinduzierter atomarer Fragmentationsprozesse ermöglicht Einblicke in die Dynamik korrelierter Mehr-Teilchen-Systeme, deren theoretische Beschreibung bis heute eine der fundamentalsten Herausforderungen der Physik darstellt. Den sensitivsten Test theoretischer Modelle erlauben kinematisch vollständige Experimente, bei denen die Impulsbilanz aller beteiligter Teilchen vermessen wird. Bei der stoßinduzierten Ionisation von Helium wurden dabei überraschende Diskrepanzen zwischen Theorie und Experiment gefunden. In Rahmen dieser Arbeit wurde zum ersten Mal eine neuartige experimentelle Technik, ein sogenanntes MOTReMi, bestehend aus einem Reaktionsmikroskop (ReMi) in Kombination mit einer magneto-optischen Falle (MOT) zur Präparation und Kühlung des Targets, verwendet und erlaubt eine Verbesserung der Rückstoßionen-Impulsauflösung verglichen mit früheren Experimenten um den Faktor 2-3. Als Target wurde Lithium aufgrund seiner interessanten elektronischen Struktur gewählt. In den in dieser Arbeit durchgeführten Experimenten am Test-Speicherring TSR wurde die Einfachionisation von Lithium im Stoß mit 6 MeV Protonen sowie mit 24 MeV O8+ -Ionen studiert, was im Rahmen einer perturbativen Beschreibung einer sehr kleinen bzw. mittleren Störung entspricht. Dabei gelang es erstmals, vollständig differentiellen Wirkungsquerschnitte für ein Target anders als Helium zu vermessen, und darüber hinaus die Ionisation eines zustands-präparierten und polarisierten Targets zu untersuchen. Es wurden Charakteristika in den vollständig differentiellen Daten gefunden, die auf Eigenschaften der Anfangszustandswellenfunktionen des Targets zurückgeführt werden

Comparison of Experimental and Theoretical Fully Differential Cross Sections for Single Ionization of the 2s and 2p States of Li By O⁸⁺ Ions

This paper presents a full three-dimensional (3D) comparison between experiment and theory for 24 MeV O8+ single ionization of the 2s ground state of lithium and the 2p excited state. Two theoretical approximations are examined: the three-body continuum distorted-wave (3DW) and three-body continuum distorted-wave-eikonal initial state (3DW-EIS). Normally, there is a significant difference between these two approaches and the 3DW-EIS is in much better agreement with experiment. In this case, there is very little difference between the two approaches and both are in very good agreement with experiment. For the excited 2p state, the 3D cross sections would exhibit a mirror symmetry about the scattering plane if all three magnetic sublevels were excited in equal proportions. For the present experiment, the 2p+1 (m=+1) sublevel is dominantly excited (quantization axis is the incident beam direction) and for this case there is a magnetic dichroism which is observed both experimentally and theoretically

Polarization and Interference Effects in Ionization of Li by Ion Impact

We present initial-state selective fully differential cross sections for ionization of lithium by 24 MeV O8+ impact. The data for ionization from the 2s and 2p states look qualitatively different from each other and from 1s ionization of He. For ionization from the 2p state, to which in our study the mL=-1 substate predominantly contributes, we observe orientational dichroism and for 2s ionization pronounced interference which we trace back to the nodal structure of the initial-state wave function

Postcollision Effects in Target Ionization by Ion Impact at Large Momentum Transfer

We have measured and calculated fully differential cross sections for target ionization in 16-MeV O7++He and 24-MeV O8++Li collisions. As in previous studies, in the case of the He target we observe a pronounced forward shift in the angular distribution of the electrons relative to the direction of the momentum transfer q at small q (q \u3c 1 a.u.). An unexpected result is that we also find a strong forward shift at large q (q \u3e 2 a.u.), while at intermediate q this shift becomes very weak or even turns into a backward shift. For the Li target, in contrast, the forward shift monotonically increases with increasing q. These observations are qualitatively reproduced by our calculations. The comparison to theory suggests that at large q the forward shift is due to the postcollision interaction between the outgoing projectile and the ejected electron, but at small q it is mostly due to an interplay between the projectile-target core interaction and the electron-target core interaction

Ion-Lithium Collision Dynamics Studied with a Laser-Cooled In-Ring Target

We present a novel experimental tool allowing for kinematically complete studies of break-up processes of laser-cooled atoms. This apparatus, the \u27MOTReMi,\u27 is a combination of a magneto-optical trap (MOT) and a reaction microscope (ReMi). Operated in an ion-storage ring, the new setup enables us to study the dynamics in swift ion-atom collisions on an unprecedented level of precision and detail. In the inaugural experiment on collisions with 1.5MeV/amu O8 +-Li the pure ionization of the valence electron as well as the ionization-excitation of the lithium target was investigated

Initial-State Selective Study of Ionization Dynamics in Ion-Li Collisions

Kinematically complete experiments were performed on the ionization of a laser-cooled lithium target from different initial states, Li(2s), Li(2p) and Li(1s), by 6 MeV H+ and 1.5 MeV amu-1 O8+ impact. In the measured doubly differential cross sections as a function of electron energy and transverse momentum transfer, a significant initial state dependence is found. Furthermore, comparison to quantum mechanical theory shows surprising discrepancies for Li(2s) and Li(1s) while there is good agreement for the Li(2p) initial state