Topic
Activated complex
About: Activated complex is a research topic. Over the lifetime, 613 publications have been published within this topic receiving 24156 citations.
Papers published on a yearly basis
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Papers
TL;DR: In this paper, a mechanism for electron transfer reactions is described, in which there is very little spatial overlap of the electronic orbitals of the two reacting molecules in the activated complex, and a quantitative theory of the rates of oxidation reduction reactions involving electron transfer in solution is presented.
Abstract: A mechanism for electron transfer reactions is described, in which there is very little spatial overlap of the electronic orbitals of the two reacting molecules in the activated complex. Assuming such a mechanism, a quantitative theory of the rates of oxidation‐reduction reactions involving electron transfer in solution is presented. The assumption of "slight‐overlap" is shown to lead to a reaction path which involves an intermediate state X* in which the electrical polarization of the solvent does not have the usual value appropriate for the given ionic charges (i.e., it does not have an equilibrium value). Using an equation developed elsewhere for the electrostatic free energy of nonequilibrium states, the free energy of all possible intermediate states is calculated. The characteristics of the most probable state are then determined with the aid of the calculus of variations by minimizing its free energy subject to certain restraints. A simple expression for the electrostatic contribution to the free energy of formation of the intermediate state from the reactants, ΔF*, is thereby obtained in terms of known quantities, such as ionic radii, charges, and the standard free energy of reaction.
This intermediate state X* can either disappear to reform the reactants, or by an electronic jump mechanism to form a state X in which the ions are characteristic of the products. When the latter process is more probable than the former, the over‐all reaction rate is shown to be simply the rate of formation of the intermediate state, namely the collision number in solution multiplied by exp(—ΔF*/kT). Evidence in favor of this is cited. In a detailed quantitative comparison, given elsewhere, with the kinetic data, no arbitrary parameters are needed to obtain reasonable agreement of calculated and experimental results.
5,953 citations
TL;DR: In this paper, the probability of the activated state is calculated using ordinary statistical mechanics, and the probability multiplied by the rate of decomposition gives the specific rate of reaction, and necessary conditions for general statistical treatment to reduce to the usual kinetic treatment are given.
Abstract: The calculation of absolute reaction rates is formulated in terms of quantities which are available from the potential surfaces which can be constructed at the present time. The probability of the activated state is calculated using ordinary statistical mechanics. This probability multiplied by the rate of decomposition gives the specific rate of reaction. The occurrence of quantized vibrations in the activated complex, in degrees of freedom which are unquantized in the original molecules, leads to relative reaction rates for isotopes quite different from the rates predicted using simple kinetic theory. The necessary conditions for the general statistical treatment to reduce to the usual kinetic treatment are given.
5,545 citations
TL;DR: In this paper, the steric and pressure effects associated with the recombination of free radicals both depend on the nature of the activated complex, and are therefore intimately related, from a consideration of the reverse process of unimolecular dissociation, some equations are derived for these properties using an extension of earlier transition state and quasi-unimolecular theories.
Abstract: The steric and pressure effects associated with the recombination of free radicals both depend on the nature of the activated complex, and are therefore intimately related. From a consideration of the reverse process of unimolecular dissociation, some equations are derived for these properties using an extension of earlier transition state and quasi‐unimolecular theories. The present formalism differs from previous formulations of the latter in a number of ways, particularly in the expression used for the density of quantum states of the high energy molecules. Subsequent applications of the theory tentatively suggest that essentially all vibrational degrees of freedom of these molecules can contribute their energy to the vibrationally excited molecules. Consequently, vibrational anharmonicity would appear to be an important factor in intramolecular energy transfer. The present paper is an extension of a previously developed theory for the recombination of methyl radicals and iodine atoms.
892 citations
TL;DR: In this article, the steric effect of pressure on the rate of free radical recombinations is investigated. But the authors focus on two main problems, namely, the magnitude of steric effects tending to reduce the rate below that calculated by the kinetic theory of collisions, and the effect of a small probability of such a process results in a reduced chance of the formation of the activated complex and thus not every collision of radical and atom is effective in producing an active molecule.
Abstract: The process of recombination of free radicals may be formally regarded as proceeding via an intermediate complex (the so-called activated complex) in
which the radicals are more or less rigidly bound together to form an “active”
molecule. The term “active” here denotes a molecule containing a large excess
of vibrational energy arising from the formation of the new bond. This excess
energy must be removed through a deactivating collision, else it will reaccumulate in the new bond, and the molecule will decompose shortly after it has been formed.
This study treats the two main problems presented by radical recombinations:
the magnitude of the steric effects tending to reduce the rate below that calculated by the kinetic theory of collisions (this effect gives rise to the so-called “steric” factor) and the effect of pressure on the rate of recombination. For example, if the activated complex is a rigid structure, i.e., the radicals are
rigidly bound together, some of the rotational degrees of freedom of the radicals in their free state must be “frozen out” into bending vibrations of the new bond so that the activated complex may be formed. The relatively small probability of such a process results in a reduced chance of the formation of the activated complex and thus not every collision of radical and atom is effective in producing an active molecule. If, on the other hand, the activated complex has a loose structure, i.e., one in which the radicals rotate freely, then there will be no such restrictions on the rate of formation of the activated complex and every collision will be effective in producing an active molecule.
645 citations
TL;DR: In this article, it was shown that the cross-sectional area of etch pits on hydrolyzed feldspar grains is of the order of 10−9 to 10−8 cm2 and that the ratio of the effective to total surface area (which may or may not change with reaction progress) ranges from <0.01 to 1, depending on the grain size, dislocation density, and the extent of comminution damage on the surfaces of the grains.
632 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2024 | 1 |
| 2022 | 2 |
| 2021 | 5 |
| 2020 | 8 |
| 2019 | 8 |
| 2018 | 10 |