Addition channel rate constant

We have calculated the addition channel rate constant using the RRKM approach to unimolecular reaction rate theory, as formulated by Troe ( ) to match RRKM results with a simpler computational approach. The pressure dependence of the addition reaction (1) can be simply decribed by a Lindemann-Hinshelwood mechanism, written most conveniently in the direction of decomposition of the stable adduct ... 

Acoustic-chemical coupling, 151-54 Activation energy, 112-13 Activation energy, reaction of NH and oxygen, 109 Addition channel rate constant, 249-54... 

As indicated by the involvement of water vapor and an inert third body, this reaction has several channels (see DeMore et al., 1997, for a review). There is both a bimolecular channel, which is pressure independent, and a termolecular channel, which is pressure dependent. In addition, the rate constant increases in the presence of gaseous water, suggesting that the reaction proceeds through a mechanism such as... 

CHEMACT A Computer Code to Estimate Rate Constants for Chemically-Activated Reactions, Dean, A. M Bozzelli, J. W. and Ritter, E. R. Combust. Sci. Tech. 80, 63-85 (1991). A computer code based on the QRRK treatment of chemical activation reactions to estimate apparent rate constants for the various channels that can result in addition, recombination, and insertion reactions. 

Thus, at 1 atm in air and 298 K, abstraction predominates. The addition channel (45b) would be expected to have a pressure dependence and a negative temperature dependence (see Chapter 5.A.2). Thus is consistent with the observation that the effective overall bimolecular rate constant in 1 atm of air decreases as the temperature increases from 250 to 310 K and that the fraction of the reaction that proceeds via (45a) increases from 0.24 to 0.87 over the same temperature range (e.g., Hynes et al., 1986). 

Atomic chlorine reacts rapidly with DMS, with an overall rate constant of (3.3 + 0.5) X 10 1(1 cm3 molecule 1 s 1 at 298 K and 700 Torr total pressure (Stickel et al., 1992). As is the case for the OH reaction, the chlorine atom reaction proceeds by two reaction channels, one an abstraction and the other addition to the sulfur atom ... 

Develop a reaction mechanism for iodine (I2-O2-H2 system) from the information in the NIST Chemical Kinetics Database [256], Start with the H2-O2 reaction subset hydrogen.mec. Using the database, identify the relevant reactions with I2. Add these reactions to the starting mechanism, including product channels and rate constants. List the additional I-containing species formed in reactions of I2. Extend the reaction mechanism with reactions of these species. Continue this procedure until reactions of all relevant iodine species in the I2-O2-H2 system is included in the mechanism. 

Rates and product selectivities 5 = ([ester product]/[acid product]) x ([water]/ [alcohol solvent] were reported for solvolyses of chloroacetyl chloride at —10 °C and phenylacetyl chloride at 0 °C in EtOH- and MeOH-water mixtures. Additional kinetic data were reported for solvolyses in acetone-water, 2,2,2-trifluoroethanol (TFE)-water, and TFE-EtOH mixtures. Selectivities and solvent effects for chloroacetyl chloride, including the kinetic solvent isotope effect (KSIE) of 2.18 for MeOH, were similar to those for solvolyses of p-nilrobcnzoyl chloride rate constants in acetone-water were consistent with a third-order mechanism, and rates and products in EtOH-and MeOH-water mixtures could be explained quantitatively by competing third-order mechanisms in which one molecule of solvent (alcohol or water) acts as a nucleophile and another acts as a general base (an addition-elimination reaction channel) (29 R = Et, Me, H).23... 

The majority of the reaction proceeds via the addition channel (b) to give a methyl hydroxycyclohexadienyl radical. Cyclohexadienyl radicals are resonance stabilized and are relatively unreactive. Typical alkyl radicals add O2 rapidly with rate constants of the order of 10 12, in contrast the reaction of cyclohexadienyl and methyl cyclohexadienyl radicals with O2 proceed with rate constants of (2 - 5) x 10 16 cm3 molecule 1 s 1 [67,68]. It can be calculated that in one atmosphere of air the cyclohexadienyl radicals have a lifetime of... 

Among benzene derivatives, halogen-substituted compounds have been extensively studied and in the structure-reactivity studies " carried out on the reaction of OH and SO with the ortho and meta isomers of dichloro and dibromobenzenes and mono-bromotoluenes, the formation of substituted hydroxycyclohexadienyl radical was observed to be the major reaction channel. The bimolecular rate constants obtained for the reaction of OH with substituted halobenzenes are in the range (1.7 to 9.3) x 10 dm mol s. The rate constants obtained are found to follow the Hammett relationship for the reaction of OH with substituted halobenzenes and the p was found to be -0.5, indicating that OH radicals react by addition to the benzene ting. 

The results of the rate constant calculations by d Anna et al,156 seem to confirm this reaction mechanism. In Fig. 25 is shown the temperature dependence of the observed and calculated rate constants. The rate constant k describes the rate of formation of the post-reaction adduct under the assumption that the pre-reactive adducts are not stabilized by collisions, whereas kadd describes the kinetics of formation of the stable pre-reactive complexes at a total pressure of 1 bar. Thus the overall rate constant for the decay of reactants (denoted in the figure by a solid line) is given by the sum k + k. The values of k predicted by d Anna et al.156 distinctly underestimate the reaction rate at low temperatures, but they approach the results of measurements at temperatures above 700 K. The limiting rate constants kadd, and kadd,0 for the addition channels were analyzed in terms of statistical unimolecular rate theory. Results of the calculations show a fall-off behavior of the reaction kinetics under typical atmospheric conditions corresponding to a total pressure of 1 bar. Therefore, all kadd values were derived from the... 

In the reduced-dimensionality space the dynamics is treated exactly, e.g.. by the quantum coupled-channel approach. The remaining degrees of freedom are described in one of several approximate ways which will be reviewed below. The advantage of this approach is that it is feasible for systems of arbitrary complexity. In addition, it enables one to calculate cross sections, rate constants, etc. that are implicitly averaged over those degrees of freedom not explicitly treated dynamically, thus enabling a direct comparison to experiments which in most cases are not fully state-resolved. The degrees of freedom which are neither state-resolved experimentally nor treated dynamically will often be the same because they are usually the low-frequency motions such as rotation which are widely populated initially and finally in a collision. In the next section we shall review the elements of this theory for reactive systems with particular emphasis on resonances. 

Here, S is the specific surface area of the catalyst, a is the conversion and F is the gas flow. The term FjS is the area velocity. The rate constant depends on the type of catalyst material, the oxygen concentration, and the temperature. Additionally, it was found that the rate constant depends on the velocity in the channels, which implies that transport phenomena have an effect on the NO conversion. 

We consider three decay channels for D in addition to injection Fluorescence (rate constant k ), intramolecular radiationless decay (rate constant k ), and energy transfer quenching within the adsorbed layer (rate constant kg) ... 

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