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  • Articles  (45)
  • 1995-1999  (43)
  • 1930-1934  (2)
  • Chemistry and Pharmacology  (45)
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  • Articles  (45)
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  • 1
    Electronic Resource
    Electronic Resource
    Electron impact ionization of the SO2 molecule (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 211-218 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report measurements of the absolute cross sections for the electron-impact ionization of SO2 from threshold to 200 eV. Absolute cross sections for the formation of the SO+2 parent ions and of the SO+, S+, O+, and O+2 fragment ions were obtained independently in two different laboratories using two different experimental techniques with uncertainties ranging from ±18% to ±25%. The level of agreement between the absolute cross sections (at 70 eV) obtained by the two techniques ranges from about 10% for SO+2 and SO+ to 20% for (S++O+2) and O+, which in all cases is well within the combined error margins of the two measurements. The high resolution capability of the mass spectrometer employed in one experiment enabled the separation of the S+ and O+2 fragment ions, which are separated by only 0.017 76 atomic mass units (amu), for the first time. The single positive ion formation is the dominant process for all observed product ions. The total single SO2 ionization cross section obtained by the two techniques agreed to within 8%. A comparison of the experimentally determined total SO2 single ionization cross sections with calculated cross sections based on a modified additivity rule revealed agreement to within 20%. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469634
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  • 2
    Electronic Resource
    Electronic Resource
    Discovery of hardest known oxide (1996)
    [s.l.] : Nature Publishing Group
    Nature 383 (1996), S. 401-401 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR á€" Microhardness measurements on synthesized samples of stishovite, a high-pressure phase of silica, show that it is the hardest oxide yet discovered. Among polycrystalline materials, its hardness (33 gigapascals, GPa) rivals those of the hardest materials. Despite many ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/383401a0
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  • 3
    Electronic Resource
    Electronic Resource
    New assignments in the UV spectroscopy of the small benzene–argonn clusters: The effects of a structure-selective vibrational predissociation (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 1676-1686 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper, new experimental results using UV spectroscopy of the small benzene–Arn clusters are presented. We have found evidence for the vibrational predissociation of the S1 state of some of these species on a nanosecond time scale and we propose a new assignment for the UV spectral features of this system. This assignment is consistent with other experimental data and it accounts additionally for the previously reported spectral anomalies, in particular the ionization potential measurements of these species. The two-color R2PI spectra performed can thus be considered as nanosecond pump–probe experiments that allow us to estimate the relaxation rate of the S1state of these clusters. The vibrational relaxation is found to be strongly size and structure dependent: The two isomers [(1/1) and (2/0)] of the n=2 species exhibit different lifetimes differing by at least one order of magnitude. The size dependence of the relaxation process within the one-sided isomer series appears also paradoxical since the relaxation rates of the (3/0) and (4/0) species are found to be smaller than that of the (2/0). These properties are discussed in relationship with the symmetry of these species. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473321
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  • 4
    Electronic Resource
    Electronic Resource
    Electrochemical tuning of the lifetime of the CO stretching vibration for CO/Pt(111) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2438-2445 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used the large electric fields at the interface of a Pt(111) electrode and an acetonitrile electrolyte solution to tune the interaction between adsorbed CO and the Pt(111) surface. The electrode potential is varied over a 2.5 Volt range. As the electrode potential is made more positive, the CO vibrational frequency increases and the vibrational lifetime decreases. Over the potential range investigated, the tuning is about 35–40 cm−1 and the lifetime varies from ≈2.1 to ≈1.5 ps. Ab initio calculations performed for CO/Cu(100) predicted the opposite trend for the lifetimes for that system [M. Head-Gordon and J. C. Jully, Chem. Phys. 175, 37 (1993)]. Within an empirical model of nonadiabatic charge transfer [B. N. J. Persson and M. Persson, Solid State Commun. 36, 175 (1980)], our observations can be explained by a decreasing 2π-derived density of states of the Pt/CO complex at the Fermi level. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470938
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  • 5
    Electronic Resource
    Electronic Resource
    P-V-T equation of state of lawsonite (1999)
    Springer
    Physics and chemistry of minerals 26 (1999), S. 406-414 
    Details
    ISSN: 1432-2021
    Keywords: Key words Lawsonite ; Equation of state ; X-ray diffraction ; High-pressure ; High-temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  A pressure-volume-temperature data set has been obtained for lawsonite [CaAl2Si2O7(OH)2.H2O], using synchrotron X-ray diffraction and an externally heated diamond anvil cell. Unit-cell volumes were measured to 9.4 GPa and 767 K by angle dispersive X-ray diffraction using imaging plates. Phase changes were not observed within this pressure-temperature range, and lawsonite compressed almost isotropically at constant temperature. The P-V-T data have been analyzed using a Birch- Murnaghan equation of state and a linear equation of state expressed as β=–1/V0 (∂V/∂P) T . At room temperature, the derived equation of state parameters are: K 0=124.1 (18) GPa K'0 set to 4) and β–1=142.0(24) GPa, respectively. Our results are intermediate between previously reported measurements. The high-temperature data show that the incompressibility of lawsonite decreases with increasing temperature to ∼500 K and then increases above. Hence, the second order temperature derivative of the bulk modulus is taken into account in the equation of state; a fit of the volume data yields K 0=123.9(18) GPa, (∂K/∂T)P=–0.111(3) GPa K–1, (∂2 K/∂T 2)P=0.28(6) 10–3 GPa K–2, α0=3.1(2) 10–5 K–1, assuming K'0=4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050201
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  • 6
    Electronic Resource
    Electronic Resource
    Immunitätszüchtung bei Tabak (1934)
    Springer
    Naturwissenschaften 22 (1934), S. 557-559 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01495111
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  • 7
    Electronic Resource
    Electronic Resource
    Freezing in confined suspensions (1997)
    Springer
    Colloid & polymer science 104 (1997), S. 81-89 
    Details
    ISSN: 1435-1536
    Keywords: Confined fluids ; freezing transitions ; colloidal suspensions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The freezing transition of hard sphere colloids confined between two parallel hard plates is studied for different plate distances ranging from one to two particle diameters. Using Monte Carlo simulations and free volume theory, the full phase diagram is obtained exhibiting solid-to-solid transitions between buckled, rhombic and layered crystals involving several triangular or square layers. While the fluid freezing transition is always strongly first order, both strong and extremely weak transitions occur between different crystalline structures. These predictions should be experimentally observable in confined suspensions of sterically stabilized or highly salted charge-stabilized colloidal particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01182418
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  • 8
    Electronic Resource
    Electronic Resource
    Polyorganosiloxane-microgels as probes for forced Rayleigh scattering (1997)
    Springer
    Colloid & polymer science 104 (1997), S. 129-131 
    Details
    ISSN: 1435-1536
    Keywords: Polyorganosiloxane ; microgels-colloids ; forced Rayleigh scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We describe the synthesis of microgel spheres of 10 nm radius which are suitable as probes to study diffusion by forced Rayleigh scattering (FRS), a holographic grating technique. Those particles are obtained by a copolycondensation in microemulsion. The main advantage of organosiloxanes compared to purely organic monomers as styrene or methacrylate is the simple chemical functionalization of the particles. A rich choice of silane monomers which may be copolycondensated with the standard monomer trimethoxymethylsilane are commercially available. One of those, chlorobenzyltrimethoxysilane, is used as a coupling agent to attach the photoreactive dye orthonitrostilbene (ONS) to the microgel spheres. All samples are characterized by light scattering, GPC and electron microscopy. In addition, we determined the content of photoreactive dye chemically attached to the spherical particles by UV/visible absorption-spectroscopy. Our nano-particles are redispersible in organic solvents such as toluene or THF up to weight fractions as high as 50 wt%. To prove applicability of the particles as FRS probes we show some preliminary results obtained from FRS measurements of highly concentrated toluene solutions (particle concentration 45–50 wt%).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01182428
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  • 9
    Electronic Resource
    Electronic Resource
    Film formation of latex dispersions observed with evanescent dynamic light scattering (1997)
    Springer
    Colloid & polymer science 104 (1997), S. 191-193 
    Details
    ISSN: 1435-1536
    Keywords: Evanescent dynamic light scattering ; colloidal dispersions ; film formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We have applied evanescent dynamic light scattering (DLS) to study the film formation of polymer latex dispersions. A dynamical glass transition is observed. When the particles fuse, the scattering rate decreases. After fusion, a new fast process (τ r 1 ms) is observed, which is not present in bulk DLS data. We attribute the process to discontinuous relaxation of surface induced stresses (transient micro-cracks).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01182447
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  • 10
    Electronic Resource
    Electronic Resource
    Cell theory for the phase diagram of hard spherocylinders (1997)
    Springer
    Colloid & polymer science 104 (1997), S. 177-179 
    Details
    ISSN: 1435-1536
    Keywords: Hard spherocylinders ; phase transitions ; cell theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A cell theory is proposed to obtain the full phase diagram of hard spherocylinders involving isotropic, nematic, smectic as well as plastic and aligned crystalline phases. Despite its conceptual and numerical simplicity this free-volume theory yields the correct topology of the phase diagram in semi-quantitative agreement with recent computer simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01182443
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