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  • Articles  (20)
  • American Institute of Physics (AIP)  (19)
  • Public Library of Science (PLoS)
  • Institute of Physics (IOP)
  • Blackwell Publishing Ltd
  • MDPI Publishing
  • Chemistry and Pharmacology  (19)
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  • Articles  (20)
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  • 1
    Electronic Resource
    Electronic Resource
    Potentials of mean force of simple ions in ambient aqueous solution. I. Three-dimensional reference interaction site model approach (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10391-10402 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We adapt the three-dimensional reference interaction site model (3D-RISM) to calculate the potentials of mean force for ion–molecular solution as a difference between the chemical potential of solvation of a cluster of solutes and of individual ones. The method yields the solvation structure around the cluster of solutes in detail. The solvation chemical potential is obtained for the three-dimensional hypernetted chain (3D-HNC) closure as well as for its partial linearization (3D-PLHNC approximation). The solvation chemical potential is obtained in a closed analytical form for both the 3D-HNC and 3D-PLHNC closures. The 3D-RISM integral equations are solved by using the supercell technique. A straightforward supercell treatment of ionic solute in polar molecular solvent leads to a big error in the potential of mean force as well as the solvation chemical potential, which for simple ions in water amounts to about 35 kcal/mol. We elaborated corrections to the 3D-RISM integral equations, alleviating the artifact of the supercell periodicity with an accuracy of 0.05 kcal/mol or better and restoring the long-range asymptotics of the solute–solvent correlation functions. The dielectrically consistent site–site RISM/HNC theory (DRISM/HNC) is employed for the solvent correlations to provide a proper description of the dielectric properties of solution. This allowed us to extend the description to solution at a finite salt concentration. We converge both the 3D-RISM and site–site DRISM integral equations by using the method of modified direct inversion in the iterative subspace. Owing to the proper initial guess of the correlation functions, iteration begins at once for a given temperature and full molecular charge, avoiding a gradual decrease of the temperature and increase of the site charges, which greatly reduces the computation time. We calculate and discuss the potentials of mean force for sodium chloride in ambient water at infinite dilution as well as at a finite concentration. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481676
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  • 2
    Electronic Resource
    Electronic Resource
    Potentials of mean force of simple ions in ambient aqueous solution. II. Solvation structure from the three-dimensional reference interaction site model approach, and comparison with simulations (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10403-10417 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We applied the three-dimensional reference interaction site model (3D-RISM) integral equation theory with the 3D hypernetted chain (3D-HNC) closure or its partial linearization (3D-PLHNC) to obtain the potentials of mean force (PMFs) and the solvation structure of sodium chloride in ambient water. The bulk solvent correlations are treated by the dielectrically consistent site–site RISM/HNC theory (DRISM/HNC) to provide a proper description of the dielectric properties of solution and to include the case of a finite salt concentration. The PMF is calculated as a difference in the solvation free energy of an ion pair and of individual ions. We obtained and analyzed in detail the PMFs and solvation structure for ion pairs of NaCl at infinite dilution and a concentration of 1 M. The results are in reasonably good agreement with molecular dynamics simulations for the same model of the solution species. Positions and orientations of water molecules in the first solvation shell around the ion pair are deduced. The short-range hydration structure of the ion pairs at infinite dilution and at moderate concentration is very similar. Ionic ordering and clustering is found in 1 M solution. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481677
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  • 3
    Electronic Resource
    Electronic Resource
    Femtosecond hole-burning spectroscopy with stimulated emission pumping and supercontinuum probing (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 1894-1900 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A novel broadband femtosecond version of the stimulated emission pumping (SEP) technique is demonstrated. A nonstationary ground state of a molecular sample in the condensed phase is prepared by two optical pulses. The first picosecond PUMP pulse resonantly excites the sample. The second femtosecond DUMP pulse, which is tuned to the molecular fluorescence band, is applied after relaxation in the excited state and creates a "particle" in the ground state and a "hole" in the excited state. The relaxation of this system is probed by a femtosecond supercontinuum. An advantage of the proposed scheme is that the hole contribution is constant for certain conditions, and hence, the transient absorption spectrum of the particle may be isolated. As an application of the technique, the ground-state evolution of coumarin 102 in acetonitrile is studied. Intramolecular vibrational redistribution (IVR), with a characteristic time τIVR∼10 fs, is observed in the frequency domain. Subsequently, the absorption band shifts to the blue and shows isosbestic points in the course of relaxation. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476766
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  • 4
    Electronic Resource
    Electronic Resource
    Self-consistent description of a metal–water interface by the Kohn–Sham density functional theory and the three-dimensional reference interaction site model (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 10095-10112 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have developed a self-consistent description of an interface between a metal and a molecular liquid by combination of the density functional theory in the Kohn–Sham formulation (KS DFT) for the electronic structure, and the three-dimensional generalization of the reference interaction site model (3D RISM) for the classical site distribution profiles of liquid. The electron and classical subsystems are coupled in the mean field approximation. The procedure takes account of many-body effects of dense fluid on the metal–liquid interactions by averaging the pseudopotentials of liquid molecules over the classical distributions of the liquid. The proposed approach is substantially less time-consuming as compared to a Car–Parrinello-type simulation since it replaces molecular dynamics with the integral equation theory of molecular liquids. The calculation has been performed for pure water at normal conditions in contact with the (100) face cubic centered (fcc) surface of a metal roughly modeled after copper. The results are in good agreement with the Car–Parrinello simulation for the same metal model. The shift of the Fermi level due to the presence of water conforms with experiment. The electron distribution near an adsorbed water molecule is affected by dense water, and so the metal–water attraction follows the shapes of the metal effective electrostatic potential. For the metal model employed, it is strongest at the hollow site adsorption positions, and water molecules are adsorbed mainly at the hollow and bridge site positions rather than over metal atoms. Layering of water molecules near the metal surface is found. In the first hydration layer, adsorbed water molecules are oriented in parallel to the surface or tilted with hydrogens mainly outwards the metal. This orientation at the potential of zero charge agrees with experiment. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478883
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  • 5
    Electronic Resource
    Electronic Resource
    The structure and adsorption of the four bonding sites model for associating fluids in disordered porous media from replica Ornstein–Zernike integral equation theory (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 8651-8661 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model for a network-forming associating fluid in which each of the particles have four sites available for bonding is considered. The model possesses liquid–gas transition in the absence of attractive long-range nonassociative interactions. We have studied the adsorption of the fluid in a disordered porous media that corresponds to an equilibrium configuration of hard spheres. The associative replica Ornstein–Zernike (ROZ) equations are solved with the Percus–Yevick (PY) and hypernetted chain (HNC) closures and with the ideal network approximation. The pair distribution functions and the structure factors have been obtained. The adsorption isotherms have been calculated using a system of hard spheres adsorbed in a hard-sphere matrix as a reference. The associative contribution to the chemical potential follows from Wertheim's thermodynamic perturbation theory, however, with monomer fraction from the solution of the ROZ equations. The liquid–vapor coexistence curve has been evaluated. We have observed shrinking of the coexistence envelope with increasing matrix density. The critical temperature and the critical density are sensitive to the density of adsorbent. Both decrease with increasing matrix density. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476295
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  • 6
    Electronic Resource
    Electronic Resource
    Semiclassical model of Λ-doublet states in diatomic molecules (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 5460-5472 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An intuitive picture of Λ-doubling in diatomic molecules is presented using a semiclassical theory. A common view of Λ-doubling as arising from electrons "lagging" behind the rotating internuclear axis is shown to be misleading; rather, the eigenfunctions are symmetric about the molecular axes and can be expressed as a superposition of pure nonrotating orbitals and travelling waves. These results are shown to be consistent with a full quantum treatment. We also examine, for the first time, time-dependent states, by monitoring expectation values of electronic- and nuclear-angular momenta. For low rotation frequency, the expectation value of the electronic-angular momentum locks onto the rotating internuclear axis, while for high rotation frequency it locks onto the space-fixed total-angular momentum axis. At intermediate frequencies is a complicated behavior. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474251
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  • 7
    Electronic Resource
    Electronic Resource
    Semiclassical picture of collision-induced Λ-doublet transitions in diatomic molecules (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 5473-5487 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate collision-induced Λ-doublet transitions in a system similar to NO+Ar, based on a semiclassical model in which nuclear motion is treated classically and electronic motion quantum mechanically. We present a picture of this process by monitoring 〈Λ〉, the expectation value of the projection of electronic orbital-angular momentum onto the molecular NO axis, over the duration of the collision. In a typical collision, the interaction with Ar would cause the electronic orbital-angular momentum to precess about the rotating NO–Ar vector. However, since this angular momentum is locked tightly to the diatomic axis, it is restricted to oscillation along this axis. This oscillation leads to transitions between Λ-doublet states. In addition to providing this physical picture of the collision process, we calculate an alignment effect of 1.2 for a hypothetical three-vector correlation experiment, neglecting spin. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474252
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  • 8
    Electronic Resource
    Electronic Resource
    Femtosecond Stokes shift in styryl dyes: Solvation or intramolecular relaxation? (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3504-3511 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Transient absorption and gain spectra of the styryl dye LDS-750 in solution have been studied by the pump/supercontinuum probe (PSCP) technique with excitation at 530 nm. The pump/probe intensity correlation width was 70 fs, providing a time resolution of 40 fs. Spectra were detected in the range 400–800 nm with 1.5 nm resolution. Before 70 fs, prominent spectral structure is observed due to resonant Raman scattering from a 1500 cm−1 active mode of the chromophore. At later time, the gain spectrum undergoes an ultrafast redshift and change of shape, with time constants of ∼200 and ∼600 fs for acetonitrile and chloroform solutions, respectively. At high pumping energy (1.2 μJ), the final emitting state is reached by internal conversion from higher electronic states without a further essential Stokes shift. The emitting state is assigned to an excited isomeric form of the molecule. At low pumping energy (0.3 μJ), the first excited electronic state isomerizes in an ultrafast process followed by a slower process, the dynamics of which is controlled by the solvent. The geometrical and electronic nature of these processes and their coupling to the solvent needs further clarification. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473447
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  • 9
    Electronic Resource
    Electronic Resource
    Self-consistent field, ab initio molecular orbital and three-dimensional reference interaction site model study for solvation effect on carbon monoxide in aqueous solution (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9463-9468 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have developed a three-dimensional (3D) extension of the reference interaction site model-self-consistent field (RISM-SCF) method to treat the electronic structure of a solvated molecule. The site–site treatment of the solute–solvent correlations involving the approximation of radial averaging constitutes a bottleneck of the RISM-SCF method, and thus lacks a 3D picture of the solvation structure for complex solutes. To resolve this problem, we devised out a 3D generalization of the RISM integral equations which yields the 3D correlation functions of interaction sites of solvent molecules around a solute of arbitrary shape. In the present article, we propose a SCF combination of the ab initio molecular orbital (MO) methods and 3D-RISM approach. A benchmark result for carbon monoxide in ambient water is also presented. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481564
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  • 10
    Electronic Resource
    Electronic Resource
    Femtosecond relaxation of 2-amino-7-nitrofluorene in acetonitrile: Observation of the oscillatory contribution to the solvent response (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 5466-5468 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Transient absorption measurements of aminonitrofluorene in acetonitrile reveal for the first time an oscillatory behavior in the dynamic Stokes shift of stimulated emission. The measured relaxation curve for the maximum of the stimulated emission band is in excellent agreement with the solvation correlation function C(t) obtained from the simple continuum theory of dipolar solvation. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477164
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