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  • 1
    Electronic Resource
    Electronic Resource
    The semirigid vibrating rotor target model for quantum polyatomic reaction dynamics (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3929-3939 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper, we present detailed quantum treatment of the semirigid vibrating rotor target (SVRT) model for reaction dynamics involving polyatomic molecules. In the SVRT model, the reacting (target) molecule is treated as a semirigid vibrating rotor which can be considered as a three-dimensional generalization of the diatomic molecule. This model provides a realistic framework to treat reaction dynamics of polyatomic systems. Using the SVRT model, it becomes computationally practical to carry out quantitatively accurate quantum dynamics calculation for a variety of dynamics problems in which the reacting molecule is a polyatomic or complex molecule. In this work, specific theoretical treatment and mathematical formulation of the SVRT model are presented for three general classes of reaction systems: (1) reaction of an atom with a polyatomic molecule (atom–polyatom reaction), (2) reaction between two polyatomic molecules (polyatom–polyatom reaction), and (3) polyatomic reaction with a rigid surface (polyatom–surface reaction). Since the number of dynamical degrees of freedom in the SVRT model for the above three classes of dynamical problems is limited, accurate quantum (both ab initio and dynamical) calculations are possible for many reactions of practical chemical interest. In this paper, a time-dependent wave packet approach is employed to implement the SVRT model for dynamics calculation of polyatomic reactions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479696
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  • 2
    Electronic Resource
    Electronic Resource
    Femtosecond studies of exciton dynamics in a novel main chain chiral conjugated poly(arylenevinylene) (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3710-3720 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The formation and decay dynamics of photogenerated excitons in an optically active poly(arylenevinylene), PAV, in solution have been studied using femtosecond transient absorption spectroscopy. Photoexcitation initially creates hot excitons which quickly (〈200 fs) relax geometrically towards the equilibrium position in the excited state. The exciton subsequently decays following a double exponential with time constants of 6.5 and 420 ps in toluene. The decays become faster (5 and 250 ps) in pyridine, indicating a dependence of the relaxation process on the solvent environment. The fast decay is attributed to vibrational relaxation and internal conversion (recombination) of the exciton from the excited to the ground electronic state through tunneling or thermal-activated barrier crossing before thermalization. The slow decay is assigned to conversion of the thermalized exciton to the ground state through both radiative and nonradiative pathways. Anisotropy decay shows a fast component (6 ps in toluene and 10 ps in pyridine) and an offset which persists up to 650 ps. Possible explanations for the fast decay include internal conversion, vibrational relaxation, conformational change, and exciton migration. The offset may decay on a longer time scale through local reorientation of the conjugation segments, exciton migration, or rotational diffusion of the polymer. Comparison to a well-studied system, MEH-PPV [poly(2-methoxy, 5-(2-ethylhexoxy)-p-phenylenevinylene], provides further insight into the relaxation mechanism of photoexcitations in this PAV polymer. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473423
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  • 3
    Electronic Resource
    Electronic Resource
    Ultraviolet photochemistry and photophysics of weakly-bound (HI)2 clusters via high-n Rydberg time-of-flight spectroscopy (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 13680-13690 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100037a016
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  • 4
    Electronic Resource
    Electronic Resource
    Low-voltage electrochromic device for photovoltaic-powered smart windows (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1226-1232 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the properties of an all-solid-state electrochromic (EC) device that can be switched over a useful range of optical transmissions with voltages below 1 V. This switching voltage is smaller than required by other solid-state EC devices reported to date. We attribute the lower-than-normal switching voltage to the use of a thermally evaporated MgF2 thin film as the lithium ion conducting layer. Electrochemical impedance spectroscopy studies show that high lithium ion conductivity and low interfacial barriers for lithium exchange with the adjacent electrochromic and ion storage layers make MgF2 a good choice for the ion conductor in EC devices. This reduction in switching voltage is a first step toward powering an EC device by an integrated semitransparent single-junction photovoltaic (PV) cell. In a side-by-side bench test, where the EC device is connected to a semitransparent a-SiC:H PV cell having on open circuit voltage of 0.87 V, a relative transmission change in the EC device of 40% is achieved in less than 60 s. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363731
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  • 5
    Electronic Resource
    Electronic Resource
    Continuing degradation of the SiO2/Si interface after hot hole stress (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 2686-2692 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article reports new experimental results on the continuing interface trap generation post-hot hole injection and investigates the generation mechanism. The generation post-hole injection is found to be two orders of magnitude slower than that post-irradiation and cannot be satisfactorily explained by the transportation of hydrogen species across the gate oxide. The role played by the recombination of trapped holes with free electrons is examined. There is a lack of correlation between the trapped hole removal and the interface trap creation, which is against the prediction of the trapped hole conversion model. The results indicate that the interface traps generated during and post-stress originate from two different defects. The defect responsible for post-stress generation is excited by hole injection and then converted into an interface trap if a positive gate bias is applied. It is found that generation in a poly-Si gated metal–oxide–semiconductor field effect transistor behaves differently from that in an Al-gated device. The possible causes for this difference are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363969
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  • 6
    Electronic Resource
    Electronic Resource
    Topological coupling in magnetic multilayer films : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5113-5115 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The role of topological coupling, the magnetostatic coupling associated with interfacial roughness in magnetic sandwich/multilayer structures, was studied both analytically and experimentally. We report the first controlled measurements of such topological coupling. A coupling field of the order of 10 Oe between magnetic layers was observed in Co/Cu/Co sandwich structures fabricated with an artificially controlled in-phase roughness of variable amplitude with a fixed period of 3.5 μm. The coupling field was compared with the value predicted by a first-order approximation model and correlated with the geometry of the structure. Scale invariance of the coupling field allows the results to be extended to ultrathin giant magnetoresistance/spin valve structures. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361319
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  • 7
    Electronic Resource
    Electronic Resource
    Nucleation of the Al4Mn alloy during containerless solidification in a drop tube (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4334-4338 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The undercooling and nucleation of Al4Mn alloy have been investigated by containerless solidification in a 1.2 m long drop tube, where molten droplets of the alloy solidified in the vacuum. Droplets in various sizes were collected at the bottom of the tube. It is found by x-ray and electron diffractions that besides the orthorhombic Al6Mn and β-Mn phases, two approximants of the decagonal quasicrystal, one approximant of the icosahedral quasicrystal and decagonal domains can be observed in the as-solidified droplets. However, due to the different cooling rate or undercooling in the samples of different sizes, the phases mentioned above will appear in different amounts. The relationship between the phase composition and the sample size is discussed on the basis of the classical nucleation and growth theories. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359457
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  • 8
    Electronic Resource
    Electronic Resource
    Photodissociation of HCl at 193.3 nm: Spin–orbit branching ratio (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 1403-1405 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: HCl was photodissociated by ultraviolet (uv) radiation at 193.3 nm. Time-of-flight spectra of the hydrogen atom fragment provided the spin–orbit state distribution of the chlorine fragment, [Cl(2P1/2)]/[Cl(2P3/2)]=0.69±0.02, in excellent agreement with recent theoretical studies. The H atom angular distribution studied by changing the uv photolysis laser polarization confirmed a dominant A 1Π←X 1Σ+ electronic transition in the photoexcitation process (β=−1.01±0.04 and β*=−0.94±0.07). © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474494
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  • 9
    Electronic Resource
    Electronic Resource
    Ultrafast electron dynamics at the liquid–metal interface: Femtosecond studies using surface plasmons in aqueous silver colloid (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3860-3866 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report direct femtosecond measurements of the dynamics of photoinduced electrons at the liquid–metal interface produced by exciting the surface plasmon band of aqueous silver colloidal particles. The electron plasma resonance created initially dephases into individually excited electrons in less than 150 fs. This is followed by a large component, fast exponential decay with a time constant of 2 ps, which is attributed to electronic energy relaxation through electron–phonon coupling. A slower 40 ps decay is also observed and attributed to subsequent cooling of the excited phonons due to phonon–solvent interaction. The decay dynamics, especially the 2 ps decay, are relatively insensitive to the solvent environment, indicating that the early time decay is dominated by the properties of the silver particles. The solvent molecules play an important role in the phonon cooling process following the electronic energy relaxation. The results show that the majority of the electrons created through photoexcitation of the plasmon band decay in less than 50 ps. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468545
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  • 10
    Electronic Resource
    Electronic Resource
    Theoretical and experimental responses for a large-aperture broadband spherical transducer probing a liquid–solid boundary (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2825-2835 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical analysis of a spherical focusing transducer for broadband acoustic microscopy is proposed. The originality of the present contribution is the particular attention we have paid to describe, as rigorously as possible, the diffraction phenomena. Our analysis starts in the harmonic domain with the well-known angular spectrum method, and then gets into the time domain. A new formulation of the angular spectrum in the focal plane has been obtained and compared to other expressions previously reported. This article is deliberately limited to isotropic semi-infinite plane reflectors in order to carry out the inverse Fourier transform in an analytical way. The analytical approach is helpful for the physical interpretation of particular interesting phenomena observed in the transient analysis. A new kind of contribution to the echographic response has been identified and named "geometrical edge waves." The weight and the arrival time of each discontinuity of the impulse response is analytically evaluated and the physical meaning of each of them is clearly established with the help of a ray model. In the last part of this article, a broadband polyvinylidene fluoride transducer excited by short pulses is used for the experimental validation of the model. The excellent quantitative agreement observed on the time waveforms confirms the efficiency of our approach both in the time domain and in the harmonic one. The comparison between theory and experiment is limited here to some typical examples, but similar results have been obtained on a wide range of defocus and for a large variety of materials. Applications for the characterization of materials will be discussed in future publications. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371131
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