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  • 1
    Electronic Resource
    Electronic Resource
    Interplay of geminate and bimolecular reactions in multistage electron and energy transfer (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2872-2880 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Within the universal integral formalism of encounter theory, we described (a) the bimolecular charge recombination that follows the geminate one beginning with photoionization and (b) bimolecular quenching of singlet and triplet excitations parallel to an inter-system crossing (ISC). In both cases the new features appear which represent either the geminate ion pair density (positive) or pair vacancies density (negative), which accounts for singlets quenched before ISC. It was justified that the shortage of near-contact excitations resulting from static singlet quenching may be built into the initial conditions for subsequent evolution of triplets and lead to the "anti-Smoluchowski time behavior" of their annihilation rate constant. However, only an integral theory can account for the same effect when singlet quenching is diffusion accelerated. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474646
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  • 2
    Electronic Resource
    Electronic Resource
    Hopping reactions of charged particles (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 2662-2669 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hopping theory of transfer reactions is essentially generalized to account for the electrostatic interaction between reactants. An application is made for a solvated electron that may be trapped by ions in the course of a random walk in liquid solutions. The hopping reaction constant differs essentially from the diffusional constant but exhibits a similar dependence on the Onsager radius: reactions with anions are strongly suppressed while reactions with cations are significantly accelerated. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473367
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  • 3
    Electronic Resource
    Electronic Resource
    Universal binary theory of photochemical charge separation and distribution (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3948-3955 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using integral formalism we developed the encounter theory of reversible photoionization followed by charge recombination. This is a problem that can not be approached with conventional (differential) formalism, unless ionization is highly exothermic and thus irreversible. In this limit, the integral theory supplemented by the recipe for calculating the ion distribution may be successfully reduced to the differential theory used in our previous work. However, there is no alternative to integral theory when ionization is quasiresonant and the back electron transfer to the excited state should be accounted for. Using the contact approximation we calculated the free-energy dependence of the Stern-Volmer constant of reversible photoionization accompanied by charge recombination. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473112
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  • 4
    Electronic Resource
    Electronic Resource
    Pump-probe spectroscopy of H-bonds as the level-crossing problem (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9796-9808 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Saturation of the H-bond absorption spectra by a strong laser field is described as a level-crossing problem with diffusional motion along the reaction coordinate. The stationary populations of the ground and excited vibronic states were found, assuming that the light induced transitions between them occur only at the point of exact resonance and the nonradiative decay of the upper state is uniform. The stationary distributions in both states are also obtained and shown to be Gaussian at slow vibrational relaxation, but essentially distorted when relaxation is faster than diffusion. The absorption spectra of the weak probe light in the frame of two-level and three-level models are calculated, which show either loss or gain in different spectral regions. The existence of bleaching and superabsorption branches in corresponding transmission spectra are confirmed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476454
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  • 5
    Electronic Resource
    Electronic Resource
    H-bond spectroscopy as the level crossing problem: Evolution of nonstationary probe spectra (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 4699-4706 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The previously developed level crossing model has been employed to study the relaxation of transmission spectra of hydrogen-bonded species. We investigated the spectral transformation after the saturation of intramolecular vibrational transition by a strong light pulse as well as the signal accumulation in the course of light action. From the shape of the transmission spectrum, composed from the negative ("superabsorption") and positive ("bleaching") components, the first moment of the latter was calculated whose shift in time provides the information about the relaxation of the H-bond to the equilibrium length. The limiting cases of long and short exciting pulse as well as fast and slow vibrational relaxation were investigated. When the latter is slow the kinetics of the first moment relaxation is similar to that obtained experimentally, especially after short pumping. On the contrary, the kinetics of signal accumulation and dissipation is better to study at long pumping when it is closer to stationary response, at any time. From this response, the signal dependence on light power can be obtained, which is the main characteristic of the saturation phenomenon. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481025
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  • 6
    Electronic Resource
    Electronic Resource
    Pump-probe spectroscopy of H-bonds: Saturation kinetics and spectral transformation during and after pumping (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 1931-1941 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The saturation kinetics of the H-bond absorption spectra in a strong laser field is described as a level-crossing problem with diffusional motion along the reaction coordinate. The full analogy with kinetics and rate of electron transfer reactions is emphasized when vibrational relaxation to the ground state is negligible. In this case, the transition rate saturates with a field strength reaching the diffusional regime limited by the friction in the ground or excited state. Taking vibrational relaxation into consideration changes qualitatively the kinetics of approaching the stationary level populations and absorption of pumping light. The fast relaxation results in significant desaturation of the light induced transitions and a shortening of the transient time. The absorption spectra of the weak probe light in the context of two-level and three-level models show either loss or gain in the red wing, as well as bleaching and superabsorption in the corresponding transmission spectra. The time evolution of these spectra, after switching the strong field on and off, was studied. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477860
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  • 7
    Electronic Resource
    Electronic Resource
    Impurity quenching of fluorescence in intense light. Violation of the Stern–Volmer law (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10930-10940 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The original integral encounter theory (IET) was used to describe the kinetics and quantum yield of fluorescence in the presence of intense pumping light. We compare the energy quenching through an impurity induced interconversion, with energy quenching produced by bimolecular charge transfer from the excited donor to the acceptor of the electron. In the former case, the convolution recipe which expresses the quantum yield via the system response to δ-pulse excitation is confirmed under special conditions, while in the latter case it was shown to not be applicable at all. By means of IET we found the stationary concentrations of excitations and ions and demonstrated the qualitative violation of the classical Stern–Volmer law at high intensity of pumping light. The modified form of this law was proposed instead and the light dependence of its constant was determined in the contact approximation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481732
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  • 8
    Electronic Resource
    Electronic Resource
    Photoconductivity and singlet oxygen generation in illuminated polymer in the air atmosphere (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2200-2209 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Our original integral encounter theory is used to describe the photoconductivity of p-phenilene vinelene (PPV) accompanied by singlet oxygen generation in the polymer volume. This theory allows calculating (a) the free carrier generation due to the forward electron transfer to oxygen from the excited singlet of PPV and (b) production of singlet oxygen by energy transfer from triplet PPV generated by intersystem crossing. We obtained the stationary concentration of the free carriers, with account of their geminate recombination before separation, as well as the stationary rate of singlet oxygen generation, affected by preliminary quenching of nearest excitations in the course of ionization. Both effects are related to off-diagonal elements of the matrix integral equations for the particle concentrations that can be represented in terms of the pair distributions of charged products and phantoms of triplet states. The stationary rate constants of electron and energy transfer can be easily obtained by the contact approximation, while the charge separation quantum yield and recombination rate constant are accessible for analytic calculations within the rectangular model of the remote reaction layer for the backward electron transfer. The suppression factor for singlet oxygen generation was obtained in the contact approximation as well as numerically for the exponential energy transfer rate. The role of the finite lifetimes of singlet and triplet excitations was especially emphasized. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479492
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  • 9
    Electronic Resource
    Electronic Resource
    Response to "Comment on ‘Negative velocity correlation in hard sphere fluid' '' [J. Chem. Phys. 103, 9512 (1995)] (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 9515-9516 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two different approaches to the velocity relaxation in dense fluid are compared in the limiting case common for both and the relationship between their major parameters is found. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469965
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  • 10
    Electronic Resource
    Electronic Resource
    Activated rotational diffusion in solids (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 10858-10865 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotation of a molecule in a solid is strongly suppressed due to the corrugated potential created by the crystal and is reduced to small librations around quasistable positions with infrequent jumps between them. We study how the interaction with the crystal vibrations influences the rotational relaxation of the molecule. A simple model, in which the molecular rotation is described by a 1-D Langevin equation, is considered. The analytic expressions for the orientational and angular momentum correlation times are obtained. The Hubbard relation, which was established for dense gases and liquids, is shown to be valid for solids in the intermediate-to-high damping regime and to be violated at sufficiently low damping. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467835
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