Laser‐induced desorption of NO from NiO(100): Ab initio calculations of potential surfaces for intermediate excited states

In order to interpret the experimental results of the state resolved UV‐laser‐induced desorption of NO from NiO(100) (rotational and vibrational populations, velocity distributions of the desorbing NO molecules, etc.), we have performed ab initio complete active space self‐consistent field (CASSCF) and configuration interaction (CI) calculations for the interaction potential between NO and the NiO(100) surface in the electronic ground state and for those excited states which are involved in the desorption process. The NiO(100)–NO distance and the tilt angle between the NO axis and the surface normal have been varied. A cluster model containing a NiO8−5‐cluster embedded in a Madelung potential has been used for representing the NiO(100) surface. The excited states which are important for the desorption process, are charge transfer states of the substrate–adsorbate system, in which one electron is transferred from the surface into the NO‐2π‐orbital. The potential curves of these excited charge transfer states show deep minima (4 eV–5 eV) at surface/NO distances which are smaller than that in the ground state. The angular dependence of these potentials behaves similar as in the ground state. A semiempirical correction to the calculated excitation energies has been added which makes use of the bulk polarization of NiO. With this correction the charge transfer states are considerably stabilized. The lowest excitation energy amounts to about 4 eV which is in reasonable agreement with the onset of the laser desorption observed experimentally at about 3.5 eV. The density of the NO−‐like states is rather high, so that probably several excited states are involved in the desorption process. The potential energy curves for all of these states are quite similar, but the transitions from the ground state into different excited charge transfer states show strongly differing oscillator strengths, which are also strongly dependent on the surface/NO distance. This fact is important for the dynamics of the deexcitation process in the sense of a selection criterion for the states involved. The magnitude of the oscillator strengths is large in comparison with the excitation of NO in the gas phase, which might be an indication for the possibility of optical excitation processes. One dimensional wave packet calculations on two potential energy curves using fixed lifetimes for the excited state in each calculation have been performed and enable us to estimate the mean lifetime of the excited state to be 15 fs≤τ≤25 fs. This implies that the dynamics of the system is dominated by the attractive part of the excited state potential

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Rezension zu: Ganz, Kathrin (2018): Die Netzbewegung: Subjektpositionen im politischen Diskurs der digitalen Gesellschaft. Opladen, Berlin, Toronto: Verlag Barbara Budrich, 310 Seiten. ISBN 978-3-8474-2139-9

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The introduction of this special issue elaborates a research perspective on the meaning and function of political protest in the context of democratic orders. Starting from the consideration that protest and democratic orders form a close interrelationship, we ask how and to what extent democracy is imagined, negotiated, and problematized within protest, and how democratic orders and politics shape the formation of protest. To this end, we argue for a combination of Democratic Theory and Social Movement Studies. Interweaving these two traditions allows for empirically saturated and theoretically sound interpretations of recent episodes of contention. With this research perspective, we not only gain a deeper understanding of protest dynamics, but also of contemporary social and political transformations within modern democratic societies

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In Städten verdichten sich wie nirgendwo sonst ökonomische, soziale und kulturelle Facetten menschlichen Zusammenlebens. Hier entstehen wirtschaftliche und kulturelle Impulse. 84 Prozent der deutschen Bevölkerung lebt in Städten. Doch sind nicht alle Städte gleichermaßen Orte von Wachstum und Innovation. Mit dem Ende der Industrialisierung und dem Übergang in die Dienstleistungsgesellschaft (vgl. Bell 1999) sind einige Städte aus dem größeren Arbeits-kreislauf der Gesellschaft herausgefallen. Sie haben aufgehört, zentrale Orte des Wirtschaftens zu sein. Ihre Bevölkerungen schrumpfen, Gebäude bleiben ungenutzt und die öffentliche Hand verfügt nur über unzureichende und schwindende Mittel, dem entgegenzuwirken. Es sind strukturschwache Städte. Kommunale Schrumpfungsprozesse sind aus dem 20. Jahrhundert kaum bekannt, obwohl zwei Kriege in Deutschland tobten und unvorstellbare Verwüstungen hinterlassen haben. (...

Theoretical Investigation of Laser Induced Desorption of Small Molecules from Oxide Surfaces: A First Principles Study

State resolved laser induced desorption of NO molecules from a NiO(100) surface is studied theoretically. A full potential energy surface for the excited state was constructed by means of ab initio cluster calculations in addition to the potential energy surface for the ground state. Multidimensional wave packet calculations on these two surfaces allow a detailed simulation of experimental observables, such as velocity distributions and desorption probabilities, on a full ab initio basis

Kommunikation im ländlichen Raum

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Hashtags, Tweets, Protest? Varianten des digitalen Aktivismus

Mit der Digitalisierung entstehen Ausdrucks- und Organisationsformen von Protest, die das Verständnis von politischer Mobilisierung herausfordern. Über Instant-Messaging, soziale Medien und alternative Plattformen bildet sich ein Eigenleben des digitalen Aktivismus heraus, das auch das Protestgeschehen auf der Straße beeinflusst. In der Sozialen Bewegungsforschung lösten die Ausdifferenzierung des digitalen Aktivismus und die komplexen Interaktionen zwischen Online- und Offlineprotest neue Debatten aus. Dieser Beitrag schlägt eine Systematisierung des Wissens zu digitalem Aktivismus vor, indem aus den Medienpraktiken der Aktivist*innen fünf Varianten vorgestellt und im Kontext jener digitalen Infrastrukturen diskutiert werden, auf die sie zurückgreifen