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  • 2000-2004  (241)
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  • 1
    Electronic Resource
    Electronic Resource
    Investigation of orbital momentum profiles of methylpropane (isobutane) by binary (e,2e) spectroscopy (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 882-888 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Momentum profiles of the valence orbitals of methylpropane, also known as isobutane (CH3CH(CH3)CH3), have been studied by using a high resolution binary (e,2e) electron momentum spectrometer (EMS), at an impact energy of 1200 eV plus the binding energy, and using symmetric noncoplanar kinematics. The coincidence energy resolution of the EMS spectrometer is 0.95 eV full width at half-maximum. The experimental momentum profiles of the valence orbitals are compared with the theoretical momentum distributions calculated using Hartree–Fock (HF) and density functional theory (DFT) methods with the two basis sets of 6-31G and 6-311++G**. The B3LYP functionals are used for the DFT calculations. In general, the experimental momentum distributions are well described by the HF and DFT calculations. The pole strengths of the main ionization peaks from the orbitals in the inner valence are estimated. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1321313
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  • 2
    Electronic Resource
    Electronic Resource
    The complex of HF2− and H2O: A theoretical study (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 5883-5890 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The complex of HF2− and H2O is studied using B3LYP, MP2, and QCISD methods. Energetics, geometries, and vibrational frequencies of the equilibrium structure and two transition states are calculated using 6-311++G(d,p), 6-311++G(2d,2p), and 6-311++G(2df,2pd) basis sets. For the equilibrium structure there is a hydrogen bond between one of the F atoms of HF2− and one of the H atoms of H2O. The two transition states are only about 0.5 kcal/mol higher. The HF2−–H2O equilibrium structure is planar and, at the B3LYP/6-311++G(2df,2pd) level, the F–H–O bond angle is nearly linear at 174.4° and the F–O distance is 2.59 Å. With zero point energy and counterpoise correction, the binding energy is 14.9 kcal/mol and the strong hydrogen bond of HF2− is weakened by 11.3 kcal/mol (25%). In HF2− the experimental F–F distance is 2.28 Å and the F–H–F bond angle is 180°. The most intense IR vibration is the F–H–F asymmetric stretch at 1331 cm−1. In HF2− the calculated F–F distance is 2.30 Å and in the HF2−–H2O equilibrium structure the F–H distance for the hydrogen bonded F atom is longer by 0.13 Å but the F–H distance for the free F atom is shorter by 0.10 Å and the F–F distance is only 0.03 Å longer. The F–H–F bond angle is very close to linear at 179.4°. The most intense IR vibration remains the F–H–F asymmetric stretch, blueshifted by 648 cm−1. The F–H–O asymmetric stretch is also an intense IR vibration, redshifted by 729 cm−1 from the O–H local mode stretch for H2O. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1398094
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  • 3
    Electronic Resource
    Electronic Resource
    Dimers of alkaline earth metal halide radicals, (MX)2 (M=Be, Mg, Ca; X=F, Cl): A theoretical study (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 1534-1538 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Alkaline earth metal halide radical dimers, (MX)2 (M=Be, Mg, Ca and X=F, Cl) have not yet been observed experimentally and their existence could be doubted since MX is known to disproportionate in the bulk. We study the (MX)2 species using DFT and MP2 methods and show that they are either thermodynamically or kinetically stable with respect to various reactions including disproportionation. Energetics, geometries, and vibrational frequencies of singlet and triplet equilibrium structures and some transition states are calculated. The ground states of (MX)2 are all singlet except (CaF)2 which is triplet and, with the possible exception of (CaF)2, the ground states have a rhombic structure in which the X atoms are shared equally with each M atom. The ionization potentials of the (MX)2 species are significantly lower than those of the corresponding MX species suggesting that their chemistry may be significantly different. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1333700
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  • 4
    Electronic Resource
    Electronic Resource
    Absorption of microwaves in La1−xSrxMnO3 manganese powders over a wide bandwidth (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 5512-5514 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present the frequency dependence of microwave-absorbing properties of La1−xSrxMnO3 (x=0.4, 0.5, 0.6, and 0.7) powders at room temperature. The absorbing properties change gradually with x in the frequency range of 8–12 GHz. The optimal absorption can be achieved for a x=0.4 sample and its microwave loss peak value is about 25 dB. Further experimental results show that the absorption can be attributed to magnetic and dielectric losses and the microwave loss peak corresponds to the maximum dielectric loss tangent tan δe near 10.5 GHz. Furthermore, the absorbing properties of the oxides mixed with carbonic fiber and Y-type planar hexagonal ferrite have been rudimentarily studied. Results show that these additives greatly enhance the microwave-absorbing properties of the oxides. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415053
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  • 5
    Electronic Resource
    Electronic Resource
    Pulsed magnetic quadrupole lenses for high rigidity beams (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 376-379 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: New pulsed magnetic quadrupole lenses have been developed that can be used to focus pulsed ion beams of high rigidity. To reach sufficiently high flux densities we built such quadrupole lenses as optimized steel-free devices. Up to now a flux density of (approximate) 12 T has been reached in a quadrupole of 22 mm aperture with a sufficient field quality. This value is higher than or comparable to values reached in superconducting quadrupole lenses or in pulsed plasma lenses. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150210
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  • 6
    Electronic Resource
    Electronic Resource
    Plasma density behavior in the Hefei tokamak-7 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2933-2938 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The density profiles were measured in the Hefei tokamak-7 (HT-7) [World Survey of Activities in Controlled Fusion Research, Nuclear Fusion Special Supplement (International Atomic Energy Agency, Vienna, 1997), p. 61] ohmic discharges by means of a new multichannel far-infrared (FIR) laser interferometer. The progress on the extension of the HT-7 ohmic discharge operation region was introduced. The experiment results at the density limit, the multifaceted asymmetric radiation from the edge (MARFE) phenomena, the rf (radio frequency) boronization experiments, and the fueling efficiency studies were reported. The plasma physics in the molecular beam injection (MBI), the pellet injection (PI), and the gas puffing (GP) fueling experiments was studied and discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874144
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  • 7
    Electronic Resource
    Electronic Resource
    Materials science Single-walled 4 Å carbon nanotube arrays (2000)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 408 (2000), S. 50-51 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Here we describe the smallest carbon nanotubes possible, prepared by the pyrolysis of tripropylamine molecules in the channels of porous zeolite AlPO4-5 (AFI) single crystals. These uniformly sized carbon nanotubes have a diameter of 0.4 nm and are the best example of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35040702
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  • 8
    Electronic Resource
    Electronic Resource
    Reactions leading to the formation and breakdown of stilpnomelane in the Otago Schist, New Zealand (2000)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 18 (2000), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Semi-pelitic rocks ranging in grade from the prehnite–pumpellyite to the greenschist facies from south-eastern Otago, New Zealand, have been investigated in order to evaluate the reactions leading to formation and breakdown of stilpnomelane. Detrital grains of mica and chlorite along with fine-grained authigenic illite and chlorite occur in lower-grade rocks with compactional fabric parallel to bedding. At higher grades, detrital grains have undergone dissolution, and metamorphic phyllosilicates have crystallized with preferred orientation (sub)parallel to bedding, leading to slaty cleavage. Stilpnomelane is found in metapelites of the pumpellyite–actinolite facies and the chlorite zone of the greenschist facies, but only rarely in the biotite zone of the greenschist facies. Illite or phengite is ubiquitous, whereas chlorite occurs only rarely with stilpnomelane upgrade of the pumpellyite-out isograd. Chemical and textural relationships suggest that stilpnomelane formed from chlorite, phengite, quartz, K-feldspar and iron oxides. Stilpnomelane was produced by grain-boundary replacement of chlorite and by precipitation from solution, overprinting earlier textures. Some relict 14 Å chlorite layers are observed by TEM to be in the process of transforming to 12 Å stilpnomelane layers. The AEM analyses show that Fe is strongly partitioned over Mg into stilpnomelane relative to chlorite (KD≈2.5) and into chlorite relative to phengite (KD≈1.9). Modified A′FM diagrams, projected from the measured phengite composition rather than from ideal KAl3Si3O10(OH)2, are used to elucidate reactions among chlorite, stilpnomelane, phengite and biotite. In addition to pressure, temperature and bulk rock composition, the stilpnomelane-in isograd is controlled by variations in K, Fe3+/Fe2+, O/OH and H2O contents, and the locus of the isograd is expected to vary in rocks of different oxidation states and permeabilities. Biotite, quartz and less phengitic muscovite form from stilpnomelane, chlorite and phengite in the biotite zone. Projection of bulk rock compositions from phengite, NaAlO2, SiO2 and H2O reveals that they lie close to the polyhedra defined by the A′FM minerals and albite. Other extended A′FM diagrams, such as one projected from phengite, NaAlO2, CaAl2O4, SiO2 and H2O, may prove useful in the evaluation of other low-grade assemblages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1525-1314.2000.00263.x
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  • 9
    Electronic Resource
    Electronic Resource
    Nonlinear optical diagnosis of oxide traps formed during reactive ion etching (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 2641-2647 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Oxide traps generated by reactive ion etching are studied using a pulsed femtosecond laser. The second harmonic generation (SHG) signal from the Si/SiO2 interface is sensitive to charged traps in the oxide. The time evolution of the SHG signal indicates that positive traps predominate. The angular dependence of the polarized signal shows that the electric field generated by the oxide traps alters the symmetry of the sample. The damage is greatest for an oxide thickness of 13 nm (for a plasma dc bias of 300 V). Thicker oxides have smaller SHG signals, presumably because the Fowler–Nordheim tunneling currents induced by plasma charging of the oxide surface are smaller. Very thin oxides also exhibit reduced damage. The time dependent SHG signals depend on the temperature of the samples; these data provide information on the trapping and detrapping of substrate electrons by oxide holes. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288168
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  • 10
    Electronic Resource
    Electronic Resource
    Photoluminescence and Raman scattering of silicon nanocrystals prepared by silicon ion implantion into SiO2 films (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1439-1442 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence (PL) and Raman spectra of silicon nanocrystals prepared by Si ion implantion into SiO2 layers on Si substrate have been measured at room temperature. Their dependence on annealing temperature was investigated in detail. The PL peaks observed in the as-implanted sample originate from the defects in SiO2 layers caused by ion implantation. They actually disappear after thermal annealing at 800 °C. The PL peak from silicon nanocrystals was observed when thermal annealing temperatures are higher than 900 °C. The PL peak is redshifted to 1.7 eV and the intensity reaches maximum at the thermal annealing temperature of 1100 °C. The characterized Raman scattering peak of silicon nanocrystals was observed by using a right angle scattering configuration. The Raman signal related to the silicon nanocrystals appears only in the samples annealed at temperature above 900 °C. It further proves the formation of silicon nanocrystals in these samples. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373836
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