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  • 1
    Electronic Resource
    Electronic Resource
    Rate coefficient calculation for diffusion-influenced reversible reactions with longer-range reactivities (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 4791-4795 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The chemically relevant so-called phenomenological forward and reverse rate coefficients of reversible bimolecular solution reactions, for nonlocal reactivities defined via attributed irreversible diffusion-kinetic schemes [W. Naumann and A. Molski, J. Chem. Phys. 103, 3474 (1995)], are exactly expressed by formal operator expressions. It is shown that this rate coefficient definition corresponds to the so-called integral encounter theory by Gopich, Kipriyanov, and Doktorov [J. Chem. Phys. 110, 10888 (1999)], an isolated reactive pair approximation. Assuming detailed balance, for the bimolecular isomerization A+B(r harp over l)B+C the operator expressions lead to exact relations with the rate coefficients of the irreversible partial reactions A+B→B+C and A+B←B+C. Generalizations of the well-known Noyes formula to reversible reactions result when the corresponding Wilemski-Fixman closure approximations of the irreversible and reversible rate coefficients are inserted. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1350577
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  • 2
    Electronic Resource
    Electronic Resource
    Reversible fluorescence quenching: Generalized Stern–Volmer equations on the basis of self-consistent quenching constant relations (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 7152-7157 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For irreversible fluorescence quenching in solution, it is shown that the kinetic prediction of the Smoluchowski approach, which is exact under target model conditions, can also be alternatively formulated in terms of well-defined non-Markovian rate equations. For the well-known superposition approximation, it is demonstrated that the definition of an approximate quenching constant by a self-consistent relation can also be formally transferred to the reversible quenching processes if only the low-density limits of the net forward rate kernels in the generalized rate equations are known. Fluorescence quenching by reversible excimer formation and by reversible excitation transfer meet this requirement due to the recent findings of several authors. It is demonstrated that the proposed quenching constant approximation procedure leads to nonlinear plots with positive curvature which correct the zeroth-order linear plots in the higher quencher concentration region. The influence of the yield-reducing back reaction effect is discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481325
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  • 3
    Electronic Resource
    Electronic Resource
    Competitive reversible binding: A theoretical study of density effects on the long-time relaxation (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 10953-10960 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Competitive reversible binding is studied for a one-dimensional continuum model. Taking the reaction as a stochastic two-state process (free or occupied binding site), from many-body equations by superposition a closed system of three coupled reactive equations is derived. Linearized versions of these equations are used to get low density approximations for the long-time kinetics. Starting point is an approximation (a) from which a Szabo–Zwanzig type t−1/2 long-time law can be followed. On the basis of an approximate relation between the state-specific distribution functions obtained in (a), a higher order in density approximation (b) is derived which prescribes a concentration effect on the long-time kinetics. According to (b) the t−1/2 law is also asymptotically valid for t→∞, but with a different concentration-dependent amplitude. For time windows in an intermediate long-time range the relaxation to equilibrium appears as satisfying a modified power law (∝ t−α with α≠1/2). These analytic results, which are interesting with respect to deviations from a predicted t−3/2 decay law observed for photoexcited proton transfer in water [D. Huppert et al., Phys. Rev. Lett. 68, 3932 (1992)], are related to recent Brownian simulations of the pseudounimolecular reaction. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467845
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  • 4
    Electronic Resource
    Electronic Resource
    Monomer–excimer kinetics in solution. I. Stochastic many-particle approach (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1511-1519 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A stochastic many-particle approach is applied to study the kinetics of reversible excimer formation in solution. Coupled dynamic equations for the macroscopic concentrations and for the radial distribution function are derived, and applied to analyze (i) time resolved kinetics after a short pulse, and (ii) steady-state kinetics. Renormalization of the phenomenological excimer dissociation rate coefficient due to nonequilibrium effects is discussed. A relation is demonstrated between steady-state, reversible monomer–excimer kinetics and irreversible fluorescence kinetics. Explicit results are given for the excimer fluorescence yield, assuming the Smoluchowski–Collins–Kimball reactivity model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467235
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  • 5
    Electronic Resource
    Electronic Resource
    Monomer–excimer kinetics in solution. II. Statistical nonequilibrium thermodynamic approach (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1520-1527 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The statistical nonequilibrium thermodynamic theory of diffusion-influenced reactions is employed to study reversible excimer formation in solution. Three types of rate coefficients for bimolecular excimer formation are discussed: (i) molecular rate coefficients defined by one-way reactive fluxes, (ii) phenomenological rate constants based on form of the macroscopic rate equations, and (iii) modified, time-dependent phenomenological rate coefficients. Relations are derived linking: (i) the molecular rate coefficients for reversible and irreversible excimer formation rates, and (ii) the steady-state molecular rate constant and the Laplace transform of the time resolved irreversible rate coefficient. The relationship between the present approach and the microscopic–stochastic theory of excimer formation is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466631
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  • 6
    Electronic Resource
    Electronic Resource
    Design and performance of a versatile, cost-effective microwave electron cyclotron resonance plasma source for surface and thin film processing : The 8th international conference on ion sources (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1177-1180 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A plasma source has been developed, which makes use of electron cyclotron microwave resonance conditions without cost-intensive tuning or other active elements. A magnetron typical of domestic microwave ovens is coupled to a cylindrical resonator of fixed dimensions. A high density plasma is maintained with permanent magnets. Sources have been designed for both high vacuum and ultrahigh vacuum environments. In the latter, microwaves are conducted by a coaxial feedthrough from the resonator to a ceramic plasma cup inside the vacuum chamber. This permits shorter working distances, resulting in higher beam densities at the sample. Ions are extracted from the plasma by grid assemblies. Beam energies are in the range from 30 to 2000 eV, with densities from a few μA/cm2 up to 10 mA/cm2, respectively. Predominantly neutral species are emitted using a specially designed, ceramic grid. Operating with O2 gas, a flux of neutral monomers of 2×1016/cm2 s has been measured by the oxidation of Ag films. The performance of the source is demonstrated in various surface and thin film processes, like ion beam sputtering, reactive ion beam deposition, as well as sputter cleaning and reactive etching of semiconductor materials. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150420
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  • 7
    Electronic Resource
    Electronic Resource
    Fluorescence quenching by reversible excimer formation: Kinetic study on the basis of generalized, non-Markovian rate equations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2414-2422 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The kinetics of fluorescence quenching by reversible excimer formation has been studied theoretically on the basis of generalized, non-Markovian rate equations derived from a diffusion-kinetic hierarchy approach in the low-reactant density limit. It is demonstrated that, in contrast to the case of reversible excitation transfer [W. Naumann, J. Chem. Phys. 110, 3926 (1999)], compact rate kernel expressions can be derived not only for contact encounters but also for more realistic, longer-range reactivities. Given as functionals of so-called phenomenological excimer formation and dissociation coefficients, the rate kernel expressions allow a critical assessment of approximations based on time-scale separation arguments. An effective excimer formation coefficient is defined, which leads to simple and physically transparent formulas for the Laplace transforms of the excited monomer and excimer concentrations. The effect of the back reaction on the total fluorescence yield is discussed. The study also includes a critical comparison to analogous results obtained for the case of reversible energy transfer quenching. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479519
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  • 8
    Electronic Resource
    Electronic Resource
    Fluorescence quenching by reversible excitation transfer: Application of a hierarchy approach to a pseudo first-order model (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3926-3937 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fluorescence quenching by reversible excitation transfer is studied for a pseudo first-order model allowing only geminate-type back transfers from the acceptor to the donor. For the theoretical treatment a diffusion-kinetic hierarchy approach is applied derived on the base of reactive many-particle equations. It is demonstrated that the obtained nonlinear system of rate and pair equations is in the low concentration limit kinetically equivalent to a description by generalized rate equations (non-Markovian approach). By introducing an effective forward transfer coefficient, analogous to the definition of phenomenological rate coefficients for other type reversible reactions, compact and physically transparent formulas for the evolution of donor and acceptor concentrations during the quenching process are derived. The fluorescence quenching constant is explicitely given for a contact transfer mechanism. It is shown that for longer range transfers the calculation of the fluorescence constant calculation results in the solution of an integral equation. Some analytically solvable limiting cases are indicated and especially a Förster-type transfer is discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478247
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  • 9
    Electronic Resource
    Electronic Resource
    Comparison of the Smoluchowski approach with modern alternative approaches to diffusion-influenced fluorescence quenching: The effect of intense excitation pulses (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 402-407 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For low intensity excitation pulses, the fluorescence intensity in the presence of quenchers is obtained, within the framework of the Smoluchowski approach, by convoluting the pulse profile with the survival probability of an excited fluorophore initially surrounded by an equilibrium distribution of quenchers. This conventional approach is generalized to handle excitation pulses of arbitrary intensity. The resulting expression is exact in the limit that the fluorophore is static and the quenchers diffuse independently. Modern alternative approaches to this problem are based either explicitely or implicitely on truncating the reduced many-particle distribution function hierarchy by means of a superposition approximation. For a delta-function excitation pulse all approaches yield the identical result. For arbitrary pulses, the modern approaches predict different, albeit numerically similar, results. This difference, however, does not constitute an improvement over the Smoluchowski approach. Rather, it is a reflexion of an additional approximation that is made in the modern approaches. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474401
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  • 10
    Electronic Resource
    Electronic Resource
    Monomer-excimer kinetics in solution. III. Generalized Smoluchowski approach (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 10050-10057 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A generalized Smoluchowski approach developed in A. Molski, Chem. Phys. 182, 203 (1994) is employed to study reversible excimer formation in solution. For contact excimer formation, relations among the rate coefficients are analyzed for three modes of excitation; initially pulsed, steady-state, and periodic. A new kinetic Laplace transform relation for the frequency domain is demonstrated in the linear harmonic regime. The Laplace transform relations between the time domain and steady states, derived in W. Naumann and A. Molski, J. Chem. Phys. 100, 1511, 1520 (1994) for interaction-free models, are shown to be also valid when the interaction forces are included. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469907
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