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  • 11
    Electronic Resource
    Electronic Resource
    Femtosecond spectroscopic study of ultrafast carrier relaxation in hydrogenated amorphous silicon a-Si:H (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1235-1239 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a study of spectral- and time-resolved reflectivity and transmission measurements on hydrogenated amorphous silicon (a-Si:H) with 50 fs time resolution. Electron-hole pairs are photoexcited into the extended states of a-Si:H by an ultrashort pump pulse at (h-dash-bar)ω=2 eV. The temporal evolution of the photoinduced optical response is studied for a broad range of excitation densities from 1018 up to 1020 cm−3, and on a timescale of up to 200 ps. The temporal evolution of the optical response is discussed in terms of recombination and trapping mechanisms for carriers in the extended states of a-Si:H.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353263
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  • 12
    Electronic Resource
    Electronic Resource
    Depolarized light scattering and dynamic shear compliance of viscoelastic liquids (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 508-514 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Efforts are made to relate the depolarized light scattering spectral power density to the dynamic shear compliance spectrum of a viscoelastic liquid. Generalized Langevin equations are used to describe the dynamics and coupling of reorientation and translational motions. It is shown that in the presence of the coupling, the depolarized scattering spectrum consists of two components; one is associated with the reorientational motion, and the other with the viscoelastic relaxation of the solution. Methods to obtain the dynamic shear compliance from the depolarized light scattering spectrum are described. It is also shown that in the limit of very slow reorientational motion, the depolarized light scattering spectrum is proportional to the imaginary part of the dynamic compliance spectrum, a result predicted by the Pockels photoelastic law.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463597
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  • 13
    Electronic Resource
    Electronic Resource
    Optical absorption probes of LixNa4−x (x=1,2): Geometry, substitution isomers, and composition-dependent electron delocalization (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4918-4923 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodepletion spectra (415–763 nm, 10 A(ring) effective resolution) were obtained for LiNa3 and Li2Na2 and compared to previous Na4 and Li4 measurements as well as to model calculations ranging from classical electrostatic to ab initio molecular orbital. Findings include (i) the assignment of planar rhombic singlet ground states for both molecules; (ii) in Li2Na2, the possibleobservation of predominantly one of three energetically close-lying planar rhombic or near rhombic substitution isomers; and (iii) in the sodium/lithium tetramer series, evidence for increasing localization of itinerant valence electrons with increasing cluster lithium content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462788
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  • 14
    Electronic Resource
    Electronic Resource
    The geometry of small fullerene cages: C20 to C70 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5007-5011 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground-state structures of small fullerenes below C70 were determined by tight-binding molecular-dynamics total energy optimization. An efficient simulated annealing scheme was used to generate closed, hollow, spheroidal cage structures for all even-numbered carbon clusters from C20 to C70. As a general trend, fullerenes prefer geometries which separate the pentagonal rings as far apart as possible. Except for C60, C70, and C50, most fullerenes have relatively low symmetries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463854
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  • 15
    Electronic Resource
    Electronic Resource
    Optical absorption spectroscopy of sodium clusters as measured by collinear molecular beam photodepletion (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 3787-3801 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collinear molecular beam photodepletion was used to obtain particle specific electronic absorption information for Na3, Na4, and Na8 in a wavelength range from 370–835 nm. We critically discuss the experimental method used and the deconvolution procedure applied to the resulting data to yield absolute absorption cross sections. The spectra contain much information on the cluster-size–dependent transition from molecular to bulk-like optical response and are interpreted in terms of various computational approaches ranging from classical electrostatic to ab initio large scale configuration interaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458765
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  • 16
    Electronic Resource
    Electronic Resource
    Holographic method for investigating the diffusion of dye molecules in the polymer host (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2603-2613 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser induced holographic grating relaxation studies of thymoquinone dissolved in amorphous poly(α-methyl styrene) have been carried out. The Onsager theory of mutual diffusion for binary and tertiary systems are utilized to analyze the shape of the diffraction intensity curve. Different line shapes that are associated with the relaxation of the diffraction intensity are interpreted in terms of the diffusion processes. Diffusion coefficients are obtained as a function of thymoquinone concentration from 0.3 to 20 wt. % at various temperatures. It is shown that at very low concentrations (less than 0.5%), the self-diffusion coefficients of the dye molecule and its photoproduct are obtained. Above 0.5% concentrations the diffusion coefficient rapidly increases with increasing dye concentration. The temperature dependence of the self-diffusion coefficient follows the Williams–Landel–Ferry equation, whereas the mutual diffusion coefficient at higher dye concentrations follows the Arrhenius equation. The self-diffusion coefficient rapidly decreases as the sample temperature is traversed across the glass transition temperature (Tg). However at finite dye concentrations there is no detectable effect owing to the onset of Tg on the mutual diffusion coefficient. The difference is attributed to the plasticizing effect of the dye molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457954
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  • 17
    Electronic Resource
    Electronic Resource
    Search for the ground-state structure of C84 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7183-7185 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a well-tested tight-binding potential, we have studied all twenty-four isolated-pentagon isomers of the C84 fullerene. Unlike C76, the helical D2 isomer of C84 is energetically very unfavorable. Two isomers which have D2 and D2d symmetries are found to be much more stable than the rest. The energies of these two isomers are so close that they may coexist in synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462532
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  • 18
    Electronic Resource
    Electronic Resource
    Photodepletion probes of Na5, Na6, and Na7. Molecular dimensionality transition (2D→3D)? (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7931-7937 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodepletion spectroscopy was used to obtain electronic absorption data for Na5, Na6, and Na7 in a wavelength range from 420–770 nm. Measurements were rationalized using several models, ranging from classical electrostatic to ab initio large-scale configuration-interaction calculations. As in previous studies of Na4, Na8, and Na20, classical Mie–Drude theory applied to appropriately dimensioned metal droplets describes the gross but not a number of fine-structure features of the spectra observed. In contrast, ab initio large-scale configuration-interaction predictions of vertical electronic excitations from specific ground-state geometries can more fully account for the measurements. Theory–experiment comparison suggests that Na6 is predominantly formed under our molecular-beam conditions in a planar or near-planar structure. In contrast, the spectrum obtained for Na7 is consistent with a three-dimensional topology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462345
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  • 19
    Electronic Resource
    Electronic Resource
    Sequential reactions of SiD0–3+ and Si2D0–6+ with disilane (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7226-7233 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Sequential reactions of SiD0–3+ and Si2D0–6+ with 10−7–10−6 Torr of disilane are described. The reactions proceed, with few exceptions, by addition of SiD2 with simultaneous loss of SiD4. The growing cluster cations decrease in reactivity with increasing size. For all reaction sequences, a terminal cluster size is reached that contains fewer than nine silicon atoms. Based on our results, we conclude that the reaction of small subsilane or disilane cations with disilane does not lead to gas phase particle formation in disilane plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463548
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  • 20
    Electronic Resource
    Electronic Resource
    Dynamic light scattering, mutual diffusion, and linear viscoelasticity of polymer solutions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 3788-3797 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical study of the dynamic light scattering spectrum from a binary solution consisting of a polymer and a small molecular weight solvent is carried out. The study is based upon a modified hydrodynamic equation previously derived from statistical mechanics by Bearman and Kirkwood for a multicomponent solution. The result shows that mutual diffusion arising from the osmotic pressure fluctuation and the viscoelasticity affecting mechanical properties of the polymer solution are, in general, mixed. The extent of mixing depends on the frequency and a coupling parameter β, which is proportional to the difference between the partial specific volume of the polymer and that of the small molecular solvent.At low frequency the coupling is negligible, and one obtains a diffusion equation with the mutual diffusion coefficient dependent only on the osmotic modulus. At the frequency in the plateau stress modulus region, the result predicts a cooperative diffusion coefficient which consists of both the osmotic modulus and the longitudinal elastic modulus of the polymer solution, provided that β=1. The result is equivalent to that previously obtained by de Gennes, assuming a transient gel network model for the semidilute polymer solution. The present calculation also provides new results for the polymer solution in which the transient gel network model is not applicable. The overall light scattering spectral density is calculated in terms of the autocorrelation functions of the local pressure and the local concentration, as well as cross correlation functions between them. The result shows that as the polymer concentration is gradually increased toward the bulk state, the concentration fluctuation spectrum losses its importance, and the pressure (or density) fluctuation spectrum dominates the overall light scattering spectral density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460829
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