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  • 11
    Electronic Resource
    Electronic Resource
    Hamiltonian mapping models of molecular fragmentation (1989)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 93 (1989), S. 6947-6957 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100356a014
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  • 12
    Electronic Resource
    Electronic Resource
    Use of pulse shaping to control the photodissociation of a diatomic molecule: preventing the best from being the enemy of the good (1991)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 8019-8027 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100174a007
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  • 13
    Electronic Resource
    Electronic Resource
    A molecular dynamics study of the packing structures in monolayers of partially fluorinated amphiphiles (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 1352-1366 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the results of molecular dynamics simulations of liquid-supported monolayers of three partially fluorinated amphiphile molecules, namely CF3(CF2)9CH2COOH, CF3(CF2)6CH2(CF2)3COOH, and CF3(CF2)6(CH2)4COOH. These studies were undertaken to provide information on the interplay between molecular flexibility and the packing structure in a monolayer so as to better interpret the results of recent experiments. The qualitative aspects of the predictions of the simulations are consistent with the recent experimental data for monolayers of CF3(CF2)9CH2COOH [S. W. Barton, A. Goudot, O. Boulassa, F. Rondelez, B. Lin, F. Novak, A. Acero, and S. A. Rice, J. Chem. Phys. 96, xxx (1992)]. In particular, the observed breakup of the homogeneous ordered monolayer into ordered islands with the same collective tilt of the molecules is correctly predicted, and the fact that the collective tilt angle is small is correctly predicted. However, the experimental and theoretical values of the tilt angles are not in quantitative agreement, which we attribute to the inadequacy of the atom–atom potentials used in the simulations. In general, for monolayers of CF3(CF2)9CH2COOH we find that the collective tilt angle predicted is a sensitive function of the area per molecule and is smaller than in monolayers of alkane alcohols and alkane acids. The results of the simulations of monolayers of other partially fluorinated species suggest that the difference in size between the fluorocarbon segments and the smaller head groups or flexible "spacer'' CH2 segments can generate subtle changes in the packing structure of a monolayer and the relative stabilities of the untilted and tilted structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462171
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  • 14
    Electronic Resource
    Electronic Resource
    Molecular dynamics studies of the liquid–vapor interface of water (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2207-2218 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the results of molecular dynamics simulations of the liquid–vapor interface of water. Two different water–water interactions were studied. The density profile of the interfacial transition region between liquid and vapor is monotone with a 10%–90% width of 3.45 A(ring), in good agreement with the value determined from x-ray reflectance measurements, namely 3.30 A(ring). The water molecules in the interface tend to lie with the HOH bisector in the plane of the surface and one OH bond pointing out of the surface. As the density falls in the transition region the tetrahedral structure of the bulk liquid breaks up and there is a tendency towards dimerization. The diffusion constant in the interfacial region is 58% larger than that in the bulk region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459891
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  • 15
    Electronic Resource
    Electronic Resource
    An interpretation of the multiple fluid–fluid transitions in liquid supported amphiphile monolayers (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 1427-1434 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We describe an extension of the generalized regular solution model of a liquid supported monolayer of long chain amphiphile molecules in which chain–chain interactions outside the surface layer are included as well as the effects of chain flexibility in the surface and in the space above the surface layer. Self-consistent equations for the distribution of molecular configurations and the surface density and pressure are derived by using a model free energy expression. Two first order fluid–fluid phase transitions are predicted for three different models for the chain–chain interactions outside the surface. These transitions are identified as the observed gas-to-"liquid-expanded'' and liquid-expanded-to-"liquid-condensed'' phase transitions in a monolayer, the first to be associated with the condensation of the in-surface portions of the amphiphile chains and the second to be associated with the condensation of the out of surface portions of the amphiphile chains. This interpretation comes from the observation of the different distributions of the molecular configurations in the coexistence regions for the two transitions and is reinforced by the analysis of the sensitivity of the equation of state to the parameters used in the model. The theory leads to a simple and qualitative but accurate physical picture of the successive fluid-fluid transitions of the monolayer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458101
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  • 16
    Electronic Resource
    Electronic Resource
    Scattering from a classically chaotic repellor (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2225-2241 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a study of the classical scattering of a point particle from three hard circular discs in a plane, which we propose as a model of an idealized unimolecular fragmentation. The system possesses a fractal and chaotic metastable classical state. On the basis of a coding of the system dynamics, we develop a method to construct the invariant probability measure and to calculate the particle escape rate, the Hausdorff dimension, the Kolmogorov–Sinai entropy per unit time and the mean largest Lyapunov exponent of the repellor. The relations between these characteristics of the system dynamics are discussed. In particular, we show that, in general, chaos inhibits escaping from the metastable state. The theory is compared with numerical simulations. We also introduce the classical tools necessary for the semiclassical quantization of the dynamics; the latter is discussed in the following paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456017
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  • 17
    Electronic Resource
    Electronic Resource
    Exact quantization of the scattering from a classically chaotic repellor (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2255-2262 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The S matrix for the scattering of a point particle from three hard discs fixed on a plane is calculated exactly using Green's theorem. The S matrix is obtained explicitly from S=I−iCM−1D, where the matrix M describes the multiple scattering between the three discs and the matrices C and D describe the free propagation from the edges of the three discs to large distances. The scattering resonances are located in the complex wave number plane as the zeros of the determinant of the matrix M, and their symmetry representations are determined. The results of this calculation are compared with the results obtained from the semiclassical approximation described in the preceding paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456019
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  • 18
    Electronic Resource
    Electronic Resource
    Semiclassical quantization of the scattering from a classically chaotic repellor (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2242-2254 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The scattering of a point particle from three hard discs in a plane is studied in the semiclassical approximation, using the Gutzwiller trace formula. Using a previously introduced coding of the classical dynamics, the needed summation over the classical periodic orbits is performed. The trace function is then given in terms of Ruelle zeta functions. A semiclassical limit upper bound is obtained on the lifetimes of the scattering resonances. This bound is larger than the classical lifetime when the classical repellor is chaotic but coincides with it when the repellor is periodic. We conclude that classical chaos dramatically influences the lifetimes of the scattering resonances. Our upper bound for the resonance lifetime is compared with the results of numerical calculation of the full quantum dynamics. The distribution of the imaginary parts of the complex wave numbers of the resonances is also calculated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456018
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  • 19
    Electronic Resource
    Electronic Resource
    Kinetics of a structural phase transition in Langmuir monolayers studied using x-ray diffraction (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2393-2397 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Frequently, time-dependent effects are seen in monolayers of amphiphilic molecules (Langmuir films) when they are compressed, so that the pressure after some time is different from that recorded immediately after compression. We have identified for the first time a microscopic relaxation mechanism in monolayers of heneicosanol (C21H43OH): namely, a transition from a uniaxially distorted ("pseudohexagonal'') structural, formed upon compression, to an undistorted hexagonal structure. For T〉20 °C we observe only an apparently hexagonal phase, while at T=5 °C we observe only an apparently stable pseudohexagonal phase. When 10≤T≤20 °C, the monolayer structure changes with time from pseudohexagonal to hexagonal. The rate at which this transformation occurs is strongly temperature dependent. We propose that the observed temperature dependence is determined by the rate of nucleation of a hexagonal phase from a metastable shear-induced structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456653
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  • 20
    Electronic Resource
    Electronic Resource
    Direct measurements of vibrational predissociation of p-difluorobenzene–argon (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5624-5641 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured rates of vibrational predissociation from 12 vibrational levels of S1 p-difluorobenzene–argon (pDFB–Ar) by time-resolved two-color multiphoton ionization. Three features of our results are particularly surprising. First, the vibrational predissociation rate does not necessarily increase with additional quanta in a given ring vibrational mode. Second, direct excitation of the presumed reaction coordinate, the van der Waals stretch, may decrease the vibrational predissociation rate. Third, pDFB mode 8 (mode 16a in the Wilson notation) shows a large vibrational frequency shift upon complexation, as in other aromatic-argon complexes, but in pDFB it is at most weakly active in vibrational predissociation, in striking contrast to the other systems. These results are inconsistent with available simple theories of vibrational predissociation. We also find that the vibrational predissociation lifetime exceeds 2.7 ns even at 1634 cm−1 excess vibrational energy, where rapid vibrational energy redistribution has been predicted. Where direct comparison is possible, the rates we measure are about 40% lower than those obtained in time-integrated experiments by Parmenter and co-workers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455569
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