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  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 4478-4485 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We investigated the vibrational energies in the 2p 2A2″ and 3d 2E″ states of the triatomic deuterium molecule D3. The experiments were performed using a fast neutral beam photoionization spectrometer recently developed at Freiburg. A depletion type optical double-resonance scheme using two pulsed dye lasers was applied. The measured vibrational frequencies of the 2p 2A2″ state of D3 are compared to those of H3 and to theoretical values calculated from an ab initio potential energy surface. The data give insight into the importance of the coupling between the valence electron and the ion core. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 8983-8988 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We consider the ultrashort pulse excitation of molecules within bound electronic states. Using ultraviolet (UV) electronic and intense pulse infrared (IR)-excitation as numerical examples we compare the approximative Gaussian wave packet (GWP)-method applied to the coherent excitation of molecules to numerically exact solutions of the time-dependent Schrödinger equation. The results imply that the short-time vibrational dynamics of molecules upon femtosecond excitation can be described accurately within the GWP-method. This especially holds for the calculation of femtosecond pump/probe signals, which are much less sensitive to the errors of the method than the wave function is. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 7958-7967 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We report first investigations of high principal quantum number Rydberg states of the neutral triatomic deuterium molecule. The experiments were performed using a fast neutral beam photoionization spectrometer recently developed at Freiburg. A fast beam of metastable D3 molecules was created by charge transfer of a D3+ beam in cesium. Rydberg states of D3 were analyzed by pulsed-laser excitation using two-photon resonance-enhanced ionization, electric field ionization and autoionization. Our data identify the 2p 2A2″(N=K=0) state of D3 to be metastable with a lifetime of about 1 μs. The spectral lines following excitation in the ultraviolet spectral range were assigned to s-type and d-type Rydberg-series converging to vibrational ground state, symmetric stretch excited and degenerate mode excited D3+ ion states. By a combination of vibrationally diagonal and non-diagonal transitions, we determined the ionization potential, the symmetric stretch and degenerate mode vibrational frequencies of the 2p 2A2″ state in D3. The data give insight into the influence of the coupling between the Rydberg electron and the ion core on the potential energy surface. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    ISSN: 1468-2982
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: This study presents the first account of the prevalence of headache syndromes, defined according to the International Headache Society criteria, in a large representative sample of the German population; 5000 persons representative of the total population were selected from 30,000 households. Subjects were requested to answer a questionnaire about headache occurrence during their lifetime. The completion rate was 81.2%. Seventy-one point four percent (n = 2902) reported a history of headache. Twenty-seven point five percent fulfilled the criteria for migraine. Thirty-eight point three percent (n = 1557) met the criteria for tension-type headache and 5.6% (n = 229) did not fulfil criteria for either migraine or tension-type headache. Significant correlations were found between the prevalence of the different headache syndromes and sociodemographic variables such as sex, age and place of residence. The prevalence of headache did not exhibit any significant differences between the various länder (states or regions) of Germany. When extrapolated to the total population these results reveal that 54 million people in Germany suffer from headache at least occasionally or persistently. These findings suggest that the magnitude of the neurological disorders, migraine and tension-type headache, is seriously underestimated and thus constitutes a major contemporary health problem.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 3620-3626 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The development and the test results of an electron-beam furnace for the later utilization in a microgravitational environment are reported. By just varying the deflection pattern by means of the electron-optical components two reference profiles, a gradient profile with a maximum slope of 220 K/cm, and a hot zone profile with a zone temperature of 1520 K could be established and maintained. A beam power of 550 W had to be applied to a sample made of massive Ta for the gradient profile, for creating a hot zone profile an input power of only 250 W onto a sample with a ceramic core was sufficient. A continuous pyrometric measurement system with a high local and time resolution has been realized. By temperature sensing of the sample with this system an intrinsic feature of electron-beam heating could be directly observed, the sharply localized energy deposition at the sample surface.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 4535-4544 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We have developed a novel photofragment spectrometer to investigate the fragmentation of neutral molecules into two, three, and more neutral fragments. The parent molecules are laser prepared in a fast beam. The photofragments are detected in coincidence by a time- and position-sensitive detector which consists of multichannel plates and delay line anodes. We have developed new electronic pulse routers which allow us to measure consecutive fragment hits with dead times as low as a few nanoseconds. A new algorithm has been developed to determine for each triple hit the momentum vectors of the three fragments from the measured arrival time differences and positions. To demonstrate the performance of the spectrometer, we have investigated two- and three-body decay processes of laser-prepared triatomic hydrogen molecules H3 into H+H2 fragment pairs as well as into three hydrogen atoms H(1s)+H(1s)+H(1s). For two-body decay of vibrationless H3 3s2A1′(N=1, K=0), we have found that the resolution in the kinetic energy release spectra is far better than that achieved in previous investigations. With the new spectrometer, kinematically complete investigations of the breakup of a neutral molecule into three neutral fragments have been performed. The final state distributions in the three body decay of laser-prepared H3 molecules show pronounced structures which give insight into the complex molecular decay mechanisms. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2601-2606 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The electronic properties of thin CdSe films prepared through physical vapor transport were investigated using photoluminescence (PL) and electronic measurements. The films were studied at each of the main preparation steps, i.e., evaporation, annealing, etching, and finally photoetching. At 3 K two distinct donor-acceptor (DA) transitions at 1.75 and 1.70 eV were found in the photoluminescence spectra in addition to deep states at about 1.55 eV at 20 K. These DA transitions which are produced mainly during the evaporation might be associated with group VII and with alkali metal impurities. After each preparation step the DA transitions change their intensities. It is shown that photoetching of the films leads to a removal of the deep centers, while the 1.75 eV transition is blue shifted. In contrast with single-crystal CdSe the intensity of the PL increases after photoetching. The results of the PL are consistent with the electronic measurements. They are explained in terms of a previously published model.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 2534-2538 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Depth distributions of energy dissipation and implantation ranges in the polymer resist polymethyl methacrylate (PMMA) have been calculated by using the TRIM computer code. The relevance of such calculations to experimentally obtained data in connection with ion-beam lithography is discussed. It is concluded that the result of the computer simulations may be of value in order to explain the responsible mechanism for the modification (solubility, erosion rate) of a resist material due to ion irradiation. Experimental results of PMMA erosion during ion irradiation are also presented, showing a strong relationship between the erosion and electronic stopping.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2679-2681 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the methods and results of a theoretical study of the diamond-cubic boron nitride [BNcub] heteroepitaxial system. We introduce a general, geometric reciprocal space technique for evaluating candidate epitaxial configurations, and a novel system of essentially geometric criteria to order them from most to least likely to occur. In the diamond- BNcub system, it is found that low index like planes require a relatively small strain of 1.37% from bulk parameters. The unlike epitaxial configuration which pairs diamond{100} with BNcub{221} and yields two-dimensional coincidence with the same strain is favored above other low index mixed configurations. The essentially geometric nature of this epitaxial system is highlighted.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 9625-9632 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We report on two different crystalline phases of tris(8-hydroxyquinoline) aluminum (Alq3) which were obtained by thermal sublimation in a horizontal glass tube. These phases are investigated by x-ray powder diffraction, Raman and infrared spectroscopy, and low temperature photoluminescence measurements. Apart from the already known α phase we could identify a new crystalline phase of Alq3 (δ-Alq3) showing blueshifted fluorescence. As compared to the α phase this new phase is characterized by a larger unit cell volume, a reduced number of Raman lines in the energy range between 70 and 700 cm−1, a blueshift of the photoluminescence maximum by about 0.2 eV, and a decreased intersystem crossing to the triplet state. These differences are interpreted in terms of the isomery of the Alq3 molecule. It is supposed that the new phase contains the facial isomer, whereas in the other phases only the meridianal isomer was reported. Low temperature photoluminescence spectra show a well-resolved vibronic progression with about the same spacing of 550 cm−1 for both crystalline phases of Alq3. Site-selective photoluminescence measurements reveal the existence of an additional redshifted featureless emission, which is ascribed to energy relaxation into low-lying states. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
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