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  • Springer Nature  (77)
  • American Institute of Physics (AIP)  (34)
  • Hindawi  (12)
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  • MDPI Publishing
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3200-3203 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that the electric field of Langmuir oscillations in a cold plasma contains a component, independent of time, setting ions in motion. Using Lagrange variables, one-dimensional dynamics of plasma in respect to the interaction between electron oscillations and ion movement is investigated. As a consequence of this interaction, the crossing of electron trajectories occurs even at small amplitudes at time tc, i.e., one-dimensional turbulence appears in the system. The expression for tc is derived. In time tc ion displacements as well as ion energy are found to depend only on the electron–ion mass relationship. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2014-10-10
    Description: The absorption spectrum of thin film CsPbCl 3 in the 2–6 eV range is studied at temperatures of 90–500 K. Sudden changes show up in the temperature dependences of the parameters of the long-wavelength exciton band (spectral position E m ( T ), half width Γ( T ), and oscillator strength f ( T )) at the first order phase transitions at 310 and 320. No phase transitions in E m ( T ), Γ( T ), and f ( T ) are detected at low temperatures. The exciton excitations in CsPbCl 3 are found to have a three-dimensional character.
    Print ISSN: 1063-777X
    Electronic ISSN: 1090-6517
    Topics: Physics
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  • 3
    Publication Date: 2014-08-30
    Description: The absorption spectrum of thin film CsPbCl 3 in the 2–6 eV range is studied at temperatures of 90–500 K. Sudden changes show up in the temperature dependences of the parameters of the long-wavelength exciton band (spectral position E m ( T ), half width Γ( T ), and oscillator strength f ( T )) at the first order phase transitions at 310 and 320. No phase transitions in E m ( T ), Γ( T ), and f ( T ) are detected at low temperatures. The exciton excitations in CsPbCl 3 are found to have a three-dimensional character.
    Print ISSN: 1063-777X
    Electronic ISSN: 1090-6517
    Topics: Physics
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  • 4
    Publication Date: 2016-10-08
    Description: A study of the absorption spectrum of thin CuPb 2 Br 7 films in the 2–6 eV spectral and 90–500 K temperature ranges. It is shown that the exciton spectrum of the compound is associated with transitions in the lead ion. The temperature dependence of the spectral position and half-width of the low-frequency exciton band contains features associated with phase transitions γ → β ( T c 1  = 159 K) and β → α ( T c 2  = 434 K) and the disordering of the cation sublattice of the compound in the transition to the superionic state.
    Print ISSN: 1063-777X
    Electronic ISSN: 1090-6517
    Topics: Physics
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  • 5
    Publication Date: 2015-09-01
    Description: A study of the absorption spectrum of thin KPb 2 Cl 5 films, in the spectral range of 2–6 eV, within the temperature interval 90–520 K. It is found that low-frequency exciton states are localized in the sublattice of the compound containing the Pb 2+ ions, and that they are excitons of intermediate coupling having a two-dimensional nature.
    Print ISSN: 1063-777X
    Electronic ISSN: 1090-6517
    Topics: Physics
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6948-6960 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: To gain insight into the mechanism of Na(3p)2P3/2→2P1/2 fine-structure transitions induced by collision with He, we monitor the expectation values of the orbital- and spin-angular momentum vectors, l and s, as a function of time along the trajectory, using a semiclassical formalism. In a typical collision, 〈s〉 remains nearly space-fixed while 〈l〉 precesses about the rotating internuclear axis. Thus, in the interaction region, the projection of 〈l〉 onto the internuclear axis, 〈λ〉, remains nearly constant, and the molecular alignment of the orbital is preserved. We show how equations of motion for the classical analogues of these expectation values agree qualitatively with the quantum equations of motion. A qualitative comparison is also made with the Cs–He system for which the spin–orbit coupling is much stronger. We calculate cross sections for Na(2P3/2)+He→Na(2P1/2)+He as a function of the alignment of the excitation laser polarization with respect to the asymptotic relative velocity vector. For stationary pumping of the excited F=3 hyperfine level, this calculation predicts that the perpendicular alignment gives a cross section which is larger by a factor of 1.8 than that obtained by parallel alignment.
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  • 7
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Ca(4p2 1D2) state is prepared in a two-step excitation with linearly polarized lasers. Two different angular wave functions are selected, Y2,0 or (Y2,−1−Y2,1)/, by using parallel or perpendicular laser polarizations, respectively. Subsequent collision with a rare gas atom (He, Ne, Ar, Kr, or Xe) populates the near-resonant Ca(3d4p 1F3) state. The dependence of the collisional energy transfer process is measured as a function of the alignment of the initial 1D2 state wave function with respect to the average relative velocity vector. The laser-selected Y2,0 and (Y2,−1−Y2,1)/ angular wave functions display dramatically different alignment dependences, which are understood by an analysis of the rotation properties of these wave functions. The relative contributions to the cross section of the individual 1D2 sublevels, ML=0, ±1, and ±2, are extracted, and these vary considerably depending on the rare gas. For He, the ML=±2 sublevel (asymptotic Δ molecular state) contributes the most to the total cross section, while for all the other rare gases, the ML=0, ±1 sublevels (asymptotic Σ and Π molecular states, respectively) are more important. The contribution of the ML=0 sublevel increases smoothly with increasing mass of the rare gas collision partner, becoming the largest contributor for Xe.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6961-6972 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present results of coupled channel quantum scattering calculations of the alignment selected j=3/2→ j=1/2 fine structure changing integral cross section for Na(2P)+He. This cross section has in the past been written in terms of a coherent sum of partial wave amplitudes, but we have found that it can be expressed in terms of an incoherent sum of partial cross sections, each labeled by the total angular momentum J and by parity. It is also possible to define an alignment selected wave function for each J such that the azimuthal average of the square of this wave function projected onto each final state is proportional to the magnitude of the partial cross section into that state. This J labeled wave function is thus clearly related to the physical measurables, and we have used it to determine propensities for preservation of asymptotically prepared alignment during collisions. Using a potential surface based on Pascale's ab initio calculations, we find that the alignment ratio σ⊥/σ(parallel) is an increasing function of energy, with a value less than unity at low energy (〈0.01 eV), but increasing quickly to a value of about 2.0 at 0.04 eV and then more slowly at higher energy, up to a value of 2.7 at 0.2 eV (the highest energy considered). Above 0.02 eV, both the alignment ratio and the alignment selected integral cross sections are in good agreement with values calculated in an accompanying semiclassical study (Kovalenko, Leone, and Delos).An examination of the J labeled alignment selected scattering wave functions and of the expectation values of 〈Ω〉, 〈Λ〉, and 〈Σ〉 indicates that at low J when the initial state is prepared with (parallel) polarization, the dominant state at short range is Σ while with ⊥ polarization the dominant state is Π (i.e., asymptotic alignment is preserved). By way of contrast, this propensity for alignment preservation is not seen if fluxes or probability densities associated with alignment selected wave functions labeled by the initial orbital quantum number l (rather than J) are considered. This l labeled result is in accord with recent work by Pouilly and Alexander, but the lack of alignment preservation in this case has no relationship with the alignment cross sections, or with the alignment selected plane wave scattering wave function, since the l labeled wave functions must be coherently combined to generate this information. The orbital scrambling found for the l labeled solutions thus is not related to measurable properties, and instead the correct picture is provided by the J labeled solutions, which do show preservation of alignment. We find that even in the J labeled picture, alignment preservation does not by itself guarantee any specific trend in the alignment ratio for the fine structure transition.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 8620-8633 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop a replica generalization of the reference interaction site model (replica RISM) integral equation theory to describe the structure and thermodynamics of quenched-annealed systems comprising polar molecular species. It provides a successful approach to realistic models of molecular liquids, and properly allows for the effect of a quenched disordered matrix on the sorbed liquid. The description can be extended to an electrolyte solution in a disordered material containing charged chemical functionalities that determine its adsorption character. The replica reference interaction site model (RISM) equations are complemented with the hypernetted chain (HNC) closure and its partial linearization (PLHNC), adequate to ionic and polar molecular liquids. In these approximations, the excess chemical potentials are derived in a closed analytical form. We extend the description to a quenched-annealed system with soft-core interaction potentials between all species, in which the liquid and matrix equilibrium distributions are characterized in general by two different temperatures. The replica RISM/PLHNC-HNC theory is applied to water sorbed in a quenched disordered microporous network of atoms associated into interconnected branched chains, with activating polar groups grafted to matrix chains. The results are in qualitative agreement with experiment for water confined in disordered materials. © 2001 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 2793-2805 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We modify the site–site as well as three-dimensional (3D) versions of the reference interaction site model (RISM) integral equations with the hypernetted chain (HNC) closures by adding a repulsive bridge correction (RBC). The RBC treats the overestimation of water ordering around a hydrophobic solute in the RISM/HNC approximation, and thus refines the entropic component in the hydration free energy. We build up the bridge functions on r−12 repulsive core potentials, and propose RBC expressions for both the site–site and 3D-RISM approaches. To provide fast calculation, we obtain the excess chemical potential of hydration by using the thermodynamic perturbation theory (TPT). The site–site RISM/HNC+RBC as well as 3D-RISM/HNC+RBC approaches are applied to calculate the structure and thermodynamics of hydration of rare gases and alkanes in ambient water. For both approaches, the RBC drastically improves the agreement of the hydration chemical potential with simulation data and provides its correct dependence on the solute size. For solutes of a nonspherical form, the 3D treatment yields the hydration structure in detail and better fits simulation results, whereas the site–site approach is essentially faster. The TPT approximation gives the hydration thermodynamics in good qualitative agreement with the exact results of the thermodynamic integration, and substantially reduces computational burden. The RBC–TPT approximation can improve the predictive capability of the hybrid algorithm of a generalized-ensemble Monte Carlo simulation combined with the site–site RISM theory, used to describe protein folding with due account for the water effect at the microscopic level. The RBC can be optimized for better fit to reference simulation data, and can be generalized for solute molecules with charged groups. © 2000 American Institute of Physics.
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