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  • Nature Publishing Group  (62)
  • American Institute of Physics (AIP)  (21)
  • Wiley-Blackwell  (21)
  • American Geophysical Union (AGU)
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  • 11
    Digitale Medien
    Digitale Medien
    The DIII-D lithium beam edge diagnostic system (abstract) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4940-4940 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We are installing a diagnostic system based on a neutral lithium beam to investigate plasma behavior in the edge region of DIII-D discharges [D. M. Thomas et al., Rev. Sci. Instrum. 61, 3040 (1990]. The system will provide neutral equivalent current densities of several mA/cm2 at beam energies from 5 to 30 keV, sufficient to penetrate several centimeters past the last closed flux surface in most of the DIII-D operating regime. Fluorescence of the beam atoms is induced by collisions with plasma particles and is a sensitive measure of the edge density behavior. The emitted 670.8-nm fluorescence is collected and coupled via fiber optics to a multichannel high-speed data acquisition system based on silicon diode detectors. Because of the favorable atomic properties of lithium (i.e., high electron impact excitation cross section, resonance wavelength well separated from Hα) we should be able to study density fluctuations in this region from an analysis of the associated fluctuations in the beam fluorescence. A description of the installed diagnostic, test stand measurements of intrinsic beam fluctuations and any initial operating experience on DIII-D will be presented. This work supported by U. S. Department of Energy Grant No. DE-FG03-90ER5408 and Contract DE-AC03-89ER51114, which support does not constitute an endorsement by DOE of views expressed in this publication.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1143502
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  • 12
    Digitale Medien
    Digitale Medien
    A CO2 laser tangential imaging system for CDX-U (abstract) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4983-4983 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In a previous paper [R. Nazikian and B. Grek, Rev. Sci. Instrum. 61, 2899 (1990)], it was shown that tangential imaging provides a powerful new technique for rendering two-dimensional images of local density fluctuations in toroidal plasma devices. The technique consists of projecting a CO2 laser beam tangent to magnetic field lines at the plasma midplane and using phase contrast or other related optical methods for imaging line integral density fluctuations. In this paper we present recent progress in the development of such an imaging system for CDX-U. The interferometer makes use of a novel variation on the Zernike phase contrast method for detecting phase variations impressed on laser beams propagating through random media. This work supported by Department of Energy contract No. DE-AC02-76-CHO-3073.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1143519
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  • 13
    Digitale Medien
    Digitale Medien
    A spectroscopic study of CaOCH3 using the pump/probe microwave and the molecular beam/optical Stark techniques (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 5283-5289 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The Stark effect on the qR22(0,0.5) (ν=17 682.9251 cm−1) and qP11(0,1.5) (ν=17 682.1966 cm−1) branch features of the (0,0) B 2A1–X 2A1 band system of calcium methoxide, CaOCH3, was measured and analyzed to give the magnitude of the permanent electronic dipole moments, |μ|, of 1.58(8) D and 1.21(5) D for the X 2A1 and B 2A1 states, respectively. The dipole moments are compared with other monovalent calcium compounds and those predicted from a simple electrostatic model. Pure rotational transitions in the X 2A1 state were recorded using the pump/probe microwave-optical double resonance technique. The proton magnetic hyperfine splitting pattern confirms a C3v symmetry of the ground electronic state. The determined Fermi contact and dipolar parameters are: aF=−0.421(27) MHz; Taa=1.070(45) MHz, and |Tbb−Tcc|=0.292(47) MHz. The latter parameter is associated with the lifting of the K-degeneracy of this symmetric top molecule and mixing the I0=1/2 and I0=3/2 levels. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.477146
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  • 14
    Digitale Medien
    Digitale Medien
    Collisional relaxation of DF(v=1) and HF(v=1) by the DF dimer (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 1340-1347 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Overtone vibration-laser double resonance measurements determine the vibrational relaxation rates of DF(v=1) and HF(v=1) by the DF dimer. Both monomers are efficiently relaxed by the dimer at a rate that is 20% of the gas kinetic rate. The similarity of the rate constants for the two systems, which have very different energy defects, indicates that the relaxation occurs by collision complex formation and energy redistribution, rather than direct vibration-to-vibration energy transfer from the monomer to the dimer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.452222
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  • 15
    Digitale Medien
    Digitale Medien
    The permanent electric dipole moments of chromium and vanadium mononitride: CrN and VN (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 881-889 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The Pe(1), F″=2.5 branch feature of the (0,0) D 3Π0e–X 3Δ1 band system of 51VN was recorded as a function of an applied static electric field. The resultant Stark splitting and shifts were analyzed giving values of 3.07(7) D and 6.1(4) D for the X 3Δ1 and D 3Π0e states, respectively, for the magnitude of the permanent electric dipole moment, |μ|. Similarly, the Ree(0.5) branch feature of the (0,0) A 4Π3/2–X 4Σ− band system of 52CrN was recorded as a function of an applied static electric field and analyzed to produce |μ| values of 2.31(4) D and 5.42(2) D for the X 4Σ− and A 4Π3/2 states, respectively. In order to facilitate the dipole moment determinations for 52CrN it was necessary to record and analyze the field free spectrum of the (0,0) A 4Π3/2–X 4Σ− subband system. A comparison of the dipole moments for the first row monoxides and mononitrides is made and trends are discussed with reference to a molecular orbital correlation scheme. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.478055
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  • 16
    Digitale Medien
    Digitale Medien
    High resolution spectroscopy of BaCH3(X˜ 2A1): Fine and hyperfine structure analysis (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 2703-2711 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The pure rotational spectrum of BaCH3(X˜ 2A1) in its ground vibrational state has been recorded using millimeter/submillimeter direct absorption techniques, the first spectroscopic information obtained for this molecule. The radical was created using Broida-type oven/d.c. discharge methods by the reaction of barium vapor and Sn(CH3)4. Twenty-eight rotational transitions of the main isotopomer 138BaCH3 were recorded, as well as five for 136BaCH3 and three for the 137BaCH3 species. Being a prolate symmetric top, K ladder structure was observed in all transitions for BaCH3, as well as fine structure splittings which arise from the unpaired electron in the molecule. For the 137Ba isotopomer, hyperfine interactions were also resolved, arising from the spin of the barium nucleus. The complete data set has been analyzed with a 2A Hamiltonian, and rotational, spin-rotational, and magnetic hyperfine/nuclear quadrupole parameters accurately determined. The fine and hyperfine structure constants established from this study suggest a predominantly ionic bond for BaCH3, but with a considerable covalent component. Structural parameters for BaCH3 derived in this work are consistent with those of other alkaline earth monomethyl species. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.475662
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  • 17
    Digitale Medien
    Digitale Medien
    Collisional energy transfer via vibrational predissociation: Relaxation of HF(v=1) by HF dimers (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1132-1137 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Overtone vibration–laser double resonance measurements determine the vibrational relaxation rate of HF(v=1) by HF dimers. Vibration-to-vibration energy transfer from the excited monomer to the dimer followed by vibrational predissociation of the dimer provides an efficient pathway for vibration-to-translation energy transfer that deexcites the monomer at 40% of the gas kinetic collision rate. Analysis of the pressure dependence of the observed decay constants using a simple kinetic model establishes a rough upper limit of 10 ns on the predissociation lifetime of the collisionally excited dimer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.449475
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  • 18
    Digitale Medien
    Digitale Medien
    A direct determination of the role of vibration-to-vibration energy transfer in HF(v=3,4) self-relaxation (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 220-226 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Overtone vibration-laser double resonance directly measures the relative importance of vibration-to-vibration and vibration-to-translation-and-rotation energy transfer for HF(v=3 and v=4) at room temperature. The fraction of HF(v) molecules relaxing by V–V energy transfer is 0.44±0.05 and 0.16±0.05 for v=3 and v=4, respectively, compared to 0.59±0.10 for v=2. These measurements show that V–T,R energy transfer is the dominant relaxation mechanism for HF(v≥3) and the observed decreased amount of V–V energy transfer for higher initially excited vibrational levels is in good agreement with a chemiluminescence measurement and several theoretical calculations. The data demonstrate that the magnitude of the energy defects for the component pathways primarily determines the energy transfer mechanism for HF(v=2–4).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.450174
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  • 19
    Digitale Medien
    Digitale Medien
    Rates and pathways of vibrational self-relaxation of HF(v=2) between 300 and 700 K (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 780-788 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The temperature dependencies of the total self-relaxation rate constants for the vibrational deactivation of HF(v=2) and HF(v=1) and the state-to-state vibration-to-vibration (V–V) and vibration-to-translation-and-rotation (V-T,R) energy transfer components of the HF(v=2) self-relaxation process are measured using the overtone vibration excitation-laser double resonance technique. The total self-relaxation rate constants vary inversely with temperature. The much weaker temperature dependence of HF(v=2) self-relaxation compared to that of HF(v=1) arises from the significant role of the V–V energy transfer route. Competition between energetics and collision duration results in a weaker inverse variation with temperature for the slightly endothermic V–V route than for the exothermic V-T,R route for HF(v=2). The branching ratio for V–V energy transfer increases slightly with temperature and the data suggest that two quantum relaxation processes constitute no more than 10% of the total self-relaxation of HF(v=2). The available temperature dependence data on self-relaxation of HF(v=1–5) form a consistent picture in which the energetics of the V–V and V-T,R relaxation pathways control their relative contributions to the total energy transfer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.448503
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  • 20
    Digitale Medien
    Digitale Medien
    Laser-assisted (1+1′)-photon ionization-detected absorption spectrum of the 3pπ 2Π state of HCO and DCO (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 8384-8395 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We re-examine the ionization-detected ultraviolet absorption spectrum of the 3pπ 2Π←X 2A′ transition in HCO and DCO using a high-power visible laser to enhance the observation of first-photon resonant features. This technique, which we term here, assisted REMPI, significantly improves the signal-to-noise ratio of the spectrum, making many weak vibronic sub-bands visible for the first time. A comprehensive fit to the structure evident in a progression of bending levels from (000) to (040) refines the assignment of Song and Cool [X. M. Song and T. A. Cool, J. Chem. Phys. 96, 8664 (1992)] to yield a set of rotational constants that vary with K in relation to v2, together with a higher-order contribution to the Renner–Teller splitting in HCO, which is mirrored in DCO for all levels but (040). The (040) band falls at a frequency that is commensurate with that of CD stretch, and Fermi resonance between 3pπ 2Π(1000)Π and the higher-energy (040) K=1(Π) component gives rise to an added splitting that increases the energy of this (040) component and causes an apparent increase in the Renner parameter. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1467329
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