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  • 1
    Article
    Article
    2013
    ISSN: 0263-2764 
    Language: English
    In: Theory, Culture & Society, November 2013, Vol.30(6), pp.132-146
    Description: Wolfgang Ernst, Professor of Media Theories at the Humboldt University in Berlin, has become known through his work on media archaeology. Hence the inclusion of this translation represents an alternative take on cultural techniques. It places the legacy of cultural studies, or Kulturwissenschaften, in an interesting tension with the different epistemological demands that technical media impose. After Vico and Dilthey, argues Ernst, we need to investigate the specific modes of knowledge that technical media propose to cultural techniques. Ernst’s media archaeology and the slightly different approach to cultural techniques found in some other contributions in this issue can be seen as two of the most intriguing ways in which current German media studies has been developing in relation to Friedrich Kittler’s impact. For Ernst, this has resulted in a more technical focus and also in the development of critiques of temporality that go beyond media history. Ernst argues that media...
    Subject(s): Cultural History ; Cultural Techniques ; Epistemology ; Media ; Media Archaeology ; Media Theory ; Temporality ; Social Sciences (General)
    ISSN: 0263-2764
    E-ISSN: 1460-3616
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  • 2
    In: Physical Chemistry Chemical Physics, 2011, Vol.13(42), pp.18762-18768
    Description: We compare the 3 4 A 1 and 4 4 B 2 states of homonuclear and heteronuclear alkali trimers formed of potassium and rubidium. The Multireference Rayleigh Schrdinger Perturbation Theory of second order is applied to obtain the corresponding adiabatic potential energy surfaces. In the case of homonuclear trimers these pairs of states correspond to the two branches of the Ee JahnTeller distorted 2 4 E state. For heteronuclear trimers, the vibrational modes Q x and Q y are no longer degenerate, but the two electronic states still show a conical intersection at obtuse (KRb 2 ) or acute (K 2 Rb) isosceles geometries. Spectroscopic consequences of this situation are discussed, vibronic spectra are predicted and compared to laser-induced fluorescence spectra obtained in helium droplet isolation spectroscopy experiments of our group.
    Subject(s): Droplets ; Helium ; Schroedinger Equation ; Trimers ; Spectroscopy ; Adiabatic Flow ; Spectra ; Nanostructure ; Miscellaneous Sciences (So);
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 3
    In: Physical Chemistry Chemical Physics, 2012, Vol.14(43), pp.15158-15165
    Description: In this work we apply density-functional theory to simulate a double-dotation of He-clusters with Rb and Xe atoms. We investigate the influence of the He droplet environment on the weak van der Waals interaction between xenon and rubidium. The heliophilic Xe resides inside the droplet, while the heliophobic Rb stays on its surface. The effect of this spatial separation, the stability of the system and its properties are discussed in the context of future experiments.
    Subject(s): Xenon ; Droplets ; Physical Chemistry ; Dopants ; Simulation ; Rubidium ; Stability ; Nanostructure ; Miscellaneous Sciences (So);
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 4
    In: Physical Chemistry Chemical Physics, 2010, Vol.12(45), pp.14861-14863
    Description: Helium nanodroplets doped with rubidium atoms are ionized by applying a resonant two-step ionization scheme. Subsequent immersion of rubidium ions is observed in time-of-flight mass spectra. While alkali-metal atoms usually desorb from the surface of a helium nanodroplet upon electronic excitation, rubidium in its excited 5 2 P 1/2 state provides an exception from this rule (Auböck et al. , Phys. Rev. Lett. , 2008, 101 , 35301). In our new experiment, Rb atoms are selectively excited either to the 5 2 P 1/2 or to the 5 2 P 3/2 state. From there they are ionized by a laser pulse. Time-of-flight mass spectra of the ionization products reveal that the intermediate population of the 5 2 P 1/2 state does not only make the ionization process Rb-monomer selective, but also gives rise to a very high yield of Rb + –He N complexes. Ions with masses of up to several thousand amu have been monitored, which can be explained by an immersion of the single Rb ion into the He nanodroplet, where most likely a snowball is formed in the center of the He nanodroplet. As the most stable position for an ion is in the center of a He nanodroplet, our results agree well with theory.
    Subject(s): Helium ; Lasers ; Ionization Processes ; Ionization ; General (551.5);
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 5
    Language: English
    In: The Journal of Chemical Physics, 14 March 2012, Vol.136(10)
    Description: A new method for stable and continuous doping of superfluid helium nanodroplets (He N ) with high-melting elements such as refractory metals is presented. The method exploits the advantages of electron bombardment heating and avoids stray fields induced by high currents or high frequency fields. It is thus especially suitable for magnetic studies of atoms and clusters in He N . The source is characterized by means of mass spectroscopic investigations of He N doped with chromium atoms and clusters. Source temperatures of up to (1650 ± 50) °C were reached and Cr clusters up to Cr 9 could be formed in He N .
    Subject(s): Articles
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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  • 6
    Language: English
    In: The Journal of Chemical Physics, 21 August 2011, Vol.135(7)
    Description: We report the non-desorption of cesium (Cs) atoms on the surface of helium nanodroplets ( \documentclass[12pt]{minimal}\begin{document}${\rm He}_{\text{N}}$\end{document} He N ) in their 6 2 P 1/2 ( 2 Π 1/2 ) state upon photo-excitation as well as the immersion of Cs + into the \documentclass[12pt]{minimal}\begin{document}${\rm He}_{\text{N}}$\end{document} He N upon photo-ionization via the 6 2 P 1/2 ( 2 Π 1/2 ) state. Cesium atoms on the surface of helium nanodroplets are excited with a laser to the 6 2 P states. We compare laser-induced fluorescence (LIF) spectra with a desorption-sensitive method (Langmuir-Taylor detection) for different excitation energies. Dispersed fluorescence spectra show a broadening of the emission spectrum only when Cs- \documentclass[12pt]{minimal}\begin{document}${\rm He}_{\text{N}}$\end{document} He N is excited with photon energies close to the atomic D 1 -line, which implies an attractive character of the excited state system (Cs*- \documentclass[12pt]{minimal}\begin{document}${\rm He}_{\text{N}}$\end{document} He N ) potential energy curve. The experimental data are compared with a calculation of the potential energy curves of the Cs atom as a function of its distance R from the center of the \documentclass[12pt]{minimal}\begin{document}${\rm He}_{\text{N}}$\end{document} He N in a pseudo-diatomic model. Calculated Franck-Condon factors for emission from the 6 2 P 1/2 ( 2 Π 1/2 ) to the 6 2 S 1/2 ( 2 Σ 1/2 ) state help to explain the experimental data. The stability of the Cs*- \documentclass[12pt]{minimal}\begin{document}${\rm He}_{\text{N}}$\end{document} He N system allows to form Cs + snowballs in the \documentclass[12pt]{minimal}\begin{document}${\rm He}_{\text{N}}$\end{document} He N , where we use the non-desorbing 6 2 P 1/2 ( 2 Π 1/2 ) state as a springboard for ionization in a two-step ionization scheme. Subsequent immersion of positively charged Cs ions is observed in time-of-flight mass spectra, where masses up to several thousand amu were monitored. Only ionization via the 6 2 P 1/2 ( 2 Π 1/2 ) state gives rise to a very high yield of immersed Cs + in contrast to an ionization scheme via the 6 2 P 3/2 ( 2 Π 3/2 ) state. When resonant two-photon ionization is applied to cesium dimers on He droplets, \documentclass[12pt]{minimal}\begin{document}${\rm Cs}_2^+$\end{document} Cs 2 + - \documentclass[12pt]{minimal}\begin{document}${\rm He}_{\text{N}}$\end{document} He N aggregates are observed in time-of-flight mass spectra.
    Subject(s): Articles
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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  • 7
    In: Physical Chemistry Chemical Physics, 2011, Vol.13(42), pp.18769-18780
    Description: Homo- and heteronuclear alkali quartet trimers of type K 3 n Rb n ( n = 0,1,2,3) formed on helium nanodroplets are probed by one-color femtosecond (fs) photoionization (PI) spectroscopy. The obtained frequencies are assigned to vibrations in different electronic states in comparison to high level ab initio calculations of the involved potentials including pronounced JahnTeller and spinorbit couplings. Despite the fact that the resulting complex vibronic structure of the heavy alkali molecules complicates the comparison of experiment and theory we find good agreement for many of the observed lines for all species.
    Subject(s): Chemistry;
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 8
    Language: English
    In: The journal of physical chemistry. A, 03 October 2013, Vol.117(39), pp.9621-5
    Description: Chromium (Cr) atoms embedded into helium nanodroplets (HeN) are ejected from the droplets upon photoexcitation. During ejection they undergo electronic relaxation resulting in bare Cr atoms in various excited states. In a study of the relaxation process we present absorption spectra observed via laser induced fluorescence and beam depletion as well as dispersed fluorescence spectra and time-resolved fluorescence measurements. Broad and shifted absorption structures were found for the strong z(7)P° ← a(7)S3 and y(7)P° ← a(7)S3 excitations from the ground state. Emission lines are, in contrast, very narrow, which indicates that fluorescence is obtained from bare excited Cr atoms after ejection. Upon excitation into the y(7)P2,3,4° states we observed fluorescence from y(7)P2°, z(5)P1,2,3°, and z(7)P2,3,4°, indicating that these states are populated by electronic relaxation during the ejection processes. Relative population ratios are obtained from the intensities of individual spectral lines....
    Subject(s): Article;
    ISSN: 1089-5639
    E-ISSN: 1520-5215
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  • 9
    Language: English
    In: The journal of physical chemistry. A, 30 June 2011, Vol.115(25), pp.7005-9
    Description: The study of small clusters is intended to fill the knowledge gap between single atoms and bulk material. He nanodroplets are an ideal matrix for preparing and investigating clusters in a superfluid environment. Alkali-metal atoms are only bound very weakly to their surface by van der Waals forces. Due to the formation process, high-spin states of alkali-metal clusters on He nanodroplets are favorably observed, which is in contrast to the abundance in other preparation processes. Until now, the prevailing opinion was that stable clusters of the heavy alkali-metal atoms, rubidium (Rb) and cesium (Cs) on He nanodroplets, are limited to 5 and 3 atoms, respectively (Schulz et al., Phys. Rev. Lett. 2004, 92, 13401). Here, we present stable complexes of Rb(n)⁺ and Cs(n)⁺ consisting of up to n = 30 atoms, with the detection of large alkali-metal clusters being strongly enhanced by one-photon ionization. Our results also suggest that we monitored both high-spin and low-spin state clusters created...
    Subject(s): Chemistry;
    ISSN: 1089-5639
    E-ISSN: 1520-5215
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  • 10
    In: Physical Chemistry Chemical Physics, 2014, Vol.16(20), pp.9469-9478
    Description: The interaction between He and Cr is investigated by means of post-HartreeFock molecular orbital theory. We analyze the influence of the van der Waals forces on the complex electronic structure of the chromium atom, starting with its septet manifold and cover the first few electronically excited states up to 30000 cm 1 . For the sake of a direct comparison with ongoing experiments on Cr-doped helium nanodroplets we extend our analysis to selected states of the quintet manifold in order to explain a non-radiating relaxation from y 7 P o to z 5 P o .
    Subject(s): Helium Nanodroplets ; Spectroscopy ; Alkali–Alkaline Earth Molecules ; Excited States ; Rubidium ; Calcium ; Ab Initio;
    ISSN: 1463-9076
    ISSN: 00222852
    E-ISSN: 1463-9084
    E-ISSN: 1096083X
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