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  • 1985-1989  (8)
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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5979-5982 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The pressure dependence of the HOMO–LUMO transition energy and the frequency of the longest wavelength longitudinal optical vibration of 45 A(ring) diameter CdSe clusters in methanol–ethanol solution have been measured up to 50 Kbar. The LO mode shifts to higher frequency at a rate of 0.43 cm−1/Kbar, which corresponds to a Grüneisen parameter of 1.1. The HOMO–LUMO transition shifts to higher energy at 4.5 meV/Kbar, yielding a deformation potential of 2.3 eV. The pressure dependence of these properties closely resemble those of the corresponding bulk solid, confirming the point of view that the lattice properties of these clusters resemble those of the bulk, even though the optical properties are quite distinct.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3587-3590 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The pressure effect on 9-hydroxyphenalenone (9-HPLN) has been investigated using Raman scattering and optical absorption techniques in a diamond anvil cell up to 70 kbar hydrostatic pressure. A pressure-induced first-order phase transition occurs near 6 kbar and the Raman data shows that the transition is to the same phase that is obtained on cooling 9-HPLN below 255 K at ambient pressure. The phase boundary has a positive slope with dT/dP=7 K/kbar. The Raman data indicate that there may be another phase change near 50 kbar. A strong and sharp Raman frequency near 12 cm−1 is observed in all the phases up to the highest pressure investigated. The weak pressure dependence of this frequency and its presence up to the highest pressure suggests that it may be a molecular mode rather than an external mode frequency. The optical absorption associated with π–π* excitation exhibits a large red shift, as expected of an aromatic molecular crystal.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 480-485 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The crystalline 1:1 complex naphthalene:octafluoronaphthalene has been investigated at high pressure under ambient temperature, and down to 10 K at ambient pressure, by Raman spectroscopy. The complex is stable in the pressure range studied, 1 to 80 kbar. The lattice mode frequencies show a strong positive pressure dependence, while the internal modes are only weakly affected. The temperature and pressure dependencies of the phonon frequencies suggest that the bonding interaction between the molecular partners is of the usual van der Waals type, and the results are in agreement with the "sublattice'' model proposed by Chen and Prasad. The mode Grüneisen γi's have been obtained from the pressure data. From the measured (∂ν/∂T)p and (∂ν/∂P)T, the "explicit,'' "implicit'' contributions have been extracted.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 1682-1687 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of pressure on the optical absorption and Raman spectra of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) and on the optical absorption edge in 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) was investigated, using a diamond anvil cell. In NTCDA the absorption edge shifts red by about 8000 cm−1 in the range 0–180 kbar and in PTCDA by about 3000 cm−1 in the range 0–60 kbar pressure. At the upper limit of pressure the materials turn black, but on release of pressure the shifts were perfectly reversible. In the case of NTCDA, where both absorption and Raman data (up to 70 kbar) were obtained, the shift in the electronic absorption has been related to a parameter proportional to the intermolecular force constant. The latter was obtained from the pressure shift of an external mode Raman frequency, which showed the largest pressure dependence. The shift, which is nonlinear with pressure, becomes linear when plotted against the square of this frequency, normalized to its ambient pressure value [ν(p)/ν(0)]2. To our knowledge, this is the first time a combined absorption and Raman study has been performed on an organic system to establish such a direct relationship between electronic absorption and intermolecular interaction. No pressure-induced phase transition was encountered in NTCDA up to 180 kbar and in PTCDA up to 60 kbar, the limits of pressure in the present study. Earlier explanations for the pressure-induced red shifts in aromatic systems are briefly discussed.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1013-1031 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article reviews mainly the use of the diamond anvil cell (DAC) for ultrahigh-pressure generation (a few hundred GPa) and the various techniques employed in studying the high-pressure behavior of solids. A brief historical introduction to devices used in the prediamond-anvil era is presented in Sec. I. The basic principles of the modern DAC, ultrahigh-pressure generation, and pressure calibration are presented. Among the techniques used, x-ray diffraction, optical spectroscopy including Raman and Brillouin spectroscopy, microscopy, electrical resistance,and Mössbauer measurements, and positron annihilation studies with the DAC are reviewed. High-temperature–high-pressure (HT–HP) and low-temperature–high-pressure (LT–HP) generation in the DAC, and the problems associated with pressure calibration under these conditions are discussed. A brief section is devoted to the sintered diamond-tipped anvil apparatus, for it offers a very convenient way of studying resistance changes and superconductivity to 50-GPa pressure at normal and at liquid-He temperatures. In Sec. IV, Raman studies on solid H2 and solid N2 to about 150 GPa, p-v studies on Xe, CsI to 50 GPa, the metallization of CsI, and superconductivity of Si high-pressure polymorphs are presented. Present trends and future possibilities for ultrahigh-pressure research are briefly set out in Sec. V.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 1208-1210 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The pressure dependence of the optical phonons in LiNbO3 to 21 GPa and in LiTaO3 to 10 GPa has been investigated by Raman spectroscopy, using the diamond anvil cell. All the observed modes increase in frequency with pressure, and no mode softening occurs. This is in contrast to the behavior observed in BaTiO3 and PbTiO3, which are well-known displacive-type ferroelectric. It is suggested that this difference in pressure behavior may stem from a different type of phase transition in LiNbO3 and LiTaO3, namely the order-disorder type.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 2124-2126 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stimulated emission, obtainable at high optical pumping levels, has been used to follow the pressure dependence of the Γ-band gap of molecular beam epitaxial In0.53Ga0.47As on (001)InP. Hydrostatic pressure was generated using a diamond anvil cell, and all measurements were made at room temperature. The gap varies sublinearly with pressure for P(approximately-greater-than)10 kbar, having an initial slope of 12.44 meV/kbar. The deviation from a linear behavior is largely due to nonlinearities in the equation of state at higher pressures. The deformation potential (Xid+ (1)/(3) Xiu−a) =−(7.79±0.4)eV, for the Γ-band gap.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 12 (1987), S. 767-774 
    ISSN: 1573-6903
    Keywords: Cyclo(His-Pro) ; TRH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Cyclo(His-Pro), or histidyl-proline diketopiperazine, is an endogenous cyclic dipeptide that is ubiquitously distributed in tissues and body fluids of both man and animals. This cyclic dipeptide is not only structurally related to thyrotropin-releasing hormone (TRH, pGlu-His-ProNH2), but it can also arise from TRH by the action of the enzyme pyroglutamate amino-peptidase (pGlu-peptidase). The data on the distribution of TRH, cyclo(His-Pro), and pGlu-peptidase under normal and abnormal conditions are summarized and potential relationships analyzed. We conclude that all of the cyclo(His-Pro) cannot be derived from TRH. Two additional sources of cyclo(His-Pro) are suggested. It is proposed that 29,247 molecular weight TRH prohormone, prepro TRH, which contains 5 copies of TRH sequence, can be processed to yield cyclo(His-Pro). Thus, both TRH and cyclo(His-Pro) share a common precursor, prepro[TRH/Cyclo(His-Pro)].
    Type of Medium: Electronic Resource
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