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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4772-4776 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A simple model is derived which, by including exit-channel effects into transition state theory (TST), allows a description of state distributions in the products of three-atom barrierless unimolecular reactions. Exit-channel effects, which reduce mainly to a transfer of energy between rotational and translational motions on the way from the transition state (TS) to the products, are described within the recently derived free-path integration model (FPIM). A transfer coefficient χ relating the magnitude of the transfer to the mechanical parameters of the system is evidenced. The model is applied to the reaction O2H→O2+H in the case where it involves small transfers; semiquantitative agreement is found with quasiclassical trajectory (QCT) calculations. However, the model fails at describing product state distributions in the case of stronger transfers, demonstrating the necessity to go beyond FPIM. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 9512-9521 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We propose a simplified version of the classical statistical theory of three-atom reactions governed by long-range forces. This version is based on a partial treatment of total angular momentum conservation. We focus the developments on the determination of the recoil energy distribution of reactions performed in supersonic crossed-beam experiment. This distribution function is directly linked to the maximum values of the moduli of rotational and orbital angular momenta of the products consistent with their recoil energy and the total angular momentum disposal. Due to the simplicity of the present version, we can pinpoint the main factors which play a role in statistical reaction dynamics. It is shown that the shape of the translational energy distribution can be estimated essentially in terms of two mechanical parameters; the first one represents the available fraction of maximum angular momentum disposal in the products and the second gives a measure of the fraction of total angular momentum due to the rotation of the newly formed bond AB. Comparisons with exact calculations and experimental results are presented. They show that in addition to being able to determine propensity rules, our simple approach can even provide satisfying quantitative results. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 3349-3364 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Our goal is to derive a simple dynamically corrected statistical treatment of state distributions in the products of triatomic unimolecular reactions involving efficient energy transfers between rotation and translation motions en route to products. For, phase space theory or the adiabatic channel model—the only statistical approaches of final state distributions—may not be applicable to such processes. We thus analyze and model how the departing atom perturbs the rotation of the diatomic molecule. Since the general problem is intricate, we limit our study to the basic, yet realistic and instructive case where the bending force is harmonic and the total angular momentum is zero. A remarkable fact is the one-to-one relation between the perturbation and a coefficient χ, related in a simple way to the mechanical parameters of the system. Transition state theory combined with our model—the linear transformation model—leads to the desired treatment of product state distributions. Its predictions are in good agreement with dynamical calculations. We also show that there is a close relation between the final shape of state distributions and the angular dependence of the potential energy at the transition state. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 9380-9389 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction N(2D)+H2(X 1Σg+)→NH(X 3Σg−)+H(2S) involves an early barrier of ∼2 kcal/mol and a significant exoergicity of ∼30 kcal/mol. Thus, for collision energies of several kcal/mol, barrier crossing leads to reaction with nearly unit probability. To our knowledge, the angular dependent line of center (ADLOC) model is to date the only one which allows the analytical formulation of the barrier overcoming cross section, identifiable here with the reaction cross section. This model, however, neglects the interaction between reagents up to the barrier top. As a consequence, it ignores the reorientation of H2 with respect to N which enhances, on average, the reactivity with respect to its predictions. The linear transformation model (LTM), recently derived in order to describe product separation in unimolecular fragmentations, is now applied to the study of reagent approach in the title reaction. The main interest of LTM is to take into account reorientation while leading to an expression of the reaction cross section as simple as the ADLOC one, but in much better agreement with dynamical calculations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 1771-1784 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper, we revisit the analysis of the classical statistical behavior of three-atom collinear exchange reactions A+BC→AB+C. We begin with the intuitive reason why the statistical assumption (all the states of the available phase space are equiprobable) can, a priori, be applied without any restriction to a collisional process. To check the validity of this hypothesis, we show that an extention of the method of Wagner and Parks allows one to compute the statistical distributions of recoil energy for reactions involving a long lifetime intermediate complex. A comparison between these numerical distributions and the theoretical ones leads to some discrepancies. In order to understand the origin of these unexpected results, we implement a numerical experiment showing that trajectories "lose the memory'' of their initial conditions in a reduced area of the region where the three atoms interact. As a consequence, the statistical assumption is only applied in this area which we call the statistical region. The agreement between the resulting theoretical distributions and the numerical ones is now very satisfactory. Thus, the statistical assumption defined above fails. This surprising result shows the originality of the statistical behavior of unbounded systems with a few degrees of freedom, as compared with the larger systems usually treated by statistical mechanics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 2929-2939 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: When the nascent products of a three-atom reaction governed by chemical forces separate, energy transfers may occur between vibrational, rotational, and translational motions. In the first part of the paper, we show from quasiclassical trajectory calculations on a model potential energy surface that (a) the vibrational energy is adiabatic on average as usually assumed in statistical theories, (b) rotational-translational energy transfer mainly favors translational motion (as was initially suggested by Marcus), but that (c) this transfer is inefficient when the product atom is sufficiently light with respect to the other two. A qualitative analysis of these findings is proposed based on arguments differing from those of Marcus, and Quack and Troe. In the second part of the paper, we extend the classical statistical formalism proposed recently by ourselves, initially limited to reactions governed by long-range forces, to the present more general case of reactions involving tight transition states and for which energy transfers are inefficient. In such a case, energy distributions at the exit transition state and in the products are the same. We focus our developments on the recoil energy distribution. Agreement between our theoretical result and the quasiclassical trajectory approach is shown to be very satisfactory. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 5040-5045 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of organic chemistry 48 (1983), S. 3315-3317 
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of organic chemistry 48 (1983), S. 4723-4727 
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0301-0104
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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