• Bulletin of the Korean Chemical Society
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• 제1권1호
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• pp.30-35
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• 1980

The thermal decomposition reaction of ethyl bromide was studied in the temperature range of 724.5-$755.1^{\circ}K$. Pressure dependence of the reaction was observed in its fall-off region. A theoretical evaluation of the rate constants was carried out adopting RRKM formulation in the region and was compared with the experimental observation.The validity of theory was also reevaluated by using the observed results. The observed activation energy in this study and Arrhenius A-factor were 51.7 kcal/mole and $10^{12.5}$, respectively. The small A-factror in the study was discussed in terms of the formation of a tight activated complex and the molecular elimination as a prevalent reaction mode.

• Bulletin of the Korean Chemical Society
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• 제13권1호
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• pp.65-70
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• 1992

The hindered internal rotation effect of methyl group on chemical reaction was studied for cis-trans isomerization reaction of 1-bromopropene system using RRKM technique. A comparative study of the isomerization rates was also performed between the rigid and allowed internal rotations. The calculated rate of rigid cis-trans isomerization of 1-bromopropene was shown to be three times higher than its other halogenated propene homologues with its internal rotations and found to be in good agreement with experimental observations. These findings could be explained reasonably well in terms of the differences of the rotational barrier heights among halogenated propenes and correlated with the relatively low internal rotation barrier of cis-1-bromopropene, 230 cal/mol, compared to those of other cis-1-halopropenes, 700-800 cal/mol, and trans-1-halopropenes, 2.0-2.4 kcal/mol.

• Bulletin of the Korean Chemical Society
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• 제4권5호
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• pp.203-208
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• 1983

A thermal decomposition of trichloroethylene was studied in the temperature range of 440-$460^{\circ}C$ by using the conventional static system. In order to investigate the pressure dependence of reaction and to eliminate free radical process, propylene was used as the bath gas. The pressure range investigated was 10∼900 Torr. The decomposition was the unimolecular dehydrochlorination and the reaction products were hydrogen chloride and dichloroacetylene. Results were interpreted in terms of the Ric-Ramsperger-Kassel-Marcus (RRKM) unimolecular rate theory and the Arrhenius parameters were determined from fall-off behaviors. The Arrhenius parameters are found to be log $A=13.8{\pm}0.2sec^{-1}$ and E = $56.6{\pm}0.7$ kcal/mole, respectively.

• Bulletin of the Korean Chemical Society
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• 제15권3호
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• pp.241-245
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• 1994

A method has been developed to estimate the kinetic energy release originating from the reverse critical energy in unimolecular ion dissociation. Contribution from the excess energy was estimated by RRKM theory, the statistical adiabatic model and the modified phase space calculation. This was subtracted from the experimental kinetic energy release distribution (KERD) via deconvolution. The present method has been applied to the KERDs in $H_2$, loss from $C_6H_6^+$ and HF loss from ${CH_2CF_2}^+$. In the present formalism, not only the energy in the reaction coordinate but also the energy in some transitional vibrational degrees of freedom at the transition state is thought to contribute to the experimental kinetic energy release. Details of the methods for treating the transitional modes are found not to be critical to the final outcome. For a reaction with small excess energy and large reverse critical energy. KERD is shown to be mainly governed by the reverse critical energy.

• Bulletin of the Korean Chemical Society
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• 제9권3호
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• pp.161-164
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• 1988

Infrared multiphoton decompositions (IRMPD) of $BrCH_2CH_2CH_2CH_2Cl$ were studied by using the pulsed $CO_2$laser. At 0.3 J laser energy the experimentally observed product ratios could be reasonably explained by the RRKM calculation with initial excitation energy of ca. 80 Kcal/mol. The pressure dependence of product yields led us to conclude that the collisional deactivation by the inert gas decreased the yield of low energy dissociation channel more significantly.

• Bulletin of the Korean Chemical Society
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• 제31권9호
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• pp.2588-2592
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• 2010

The potential energy surfaces (PESs) for the primary and secondary dissociations of the phenylarsane molecular ion (1a) were determined from the quantum chemical calculations using the G3(MP2)//B3LYP method. Several pathways for the loss of $H{\cdot}$ were determined and occurred though rearrangements as well as through direct bond cleavages. The kinetic analysis based on the PES for the primary dissociation showed that the loss of $H_2$ was more favored than the loss of $H{\cdot}$, but the $H{\cdot}$. loss competed with the $H_2$ loss at high energies. The bicyclic isomer, 7-arsa-norcaradiene radical cation, was formed through the 1,2 shift of an $\alpha$-H of 1a and played an important role as an intermediate for the further rearrangements in the loss of $H{\cdot}$ and the losses of $As{\cdot}$ and AsH. The reaction pathways for the formation of the major products in the secondary dissociations of $[M-H]^+$ and $[M-H_2]^{+\cdot}$. were examined. The theoretical prediction explained the previous experimental results for the dissociation at high energies but not the dissociation at low energies.

• Bulletin of the Korean Chemical Society
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• 제10권3호
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• pp.262-269
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• 1989

The gas phase thermal decomposition of 1-bromo-3-chloropropane in the presence of radical inhibitor was studied by using the conventional static system. The mechanism of unimolecular elimination channel is shown below. [...] In this scheme, the total molecular dissociation rate constant, ($k_1\;+\;k_2$), for the decomposition of $BrCH_2CH_2CH_2Cl$ was determined by pyrolyzing the $BrCH_2CH_2CH_2Cl$ in the temperature range of $380-420^{\circ}C$ and in the pressure range of 10∼100 torr. To obtain $k_3\;and\;k_4,\;and\;to\;obtain\;k_1\;and\;k_2$ independently, the thermal decompositions of allyl chloride and allyl bromide were also studied. The Arrhenius parameters for each step are as follows; $log\;A_{\infty}\;=\;14.20(sec^{-1}),\;E_a$ = 56.10(kcal/mol) for reaction path 1; $log\;A_{\infty}\;=\;12.54(sec^{-1}),\;E_a$ = 49.75(kcal/mol) for reaction path 2; $log\;A_{\infty}\;=\;13.41(sec^{-1}),\;E_a$ = 50.04(kcal/mol) for reaction path 3; $log\;A_{\infty}\;=\;12.43(sec^{-1}),\;E_a$ = 52.78(kcal/mol) for reaction path 4; Finally, the experimentally observed pressure dependence of the rate constants in each step is compared with the theoretically predicted values that are obtained by the RRKM calculations.

• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.833-838
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• 2014

The energy- and time-dependent branching to the competing dissociation paths are studied by theory for coupled unimolecular dissociations of the o-, m-, and p-chlorotoluene radical cations to $C_7{H_7}^+$ (benzylium and tropylium). There are four different paths to $C_7{H_7}^+$, three to the benzylium ion and one to the tropylium ion, and all of them are coupled together. The branching to the multiple paths leads to the multiexponential decay of reactant with the branching ratio depending on both internal energy and time. To gain insights into the multipath branching, we study the detailed kinetics as a function of time and internal energy on the basis of ab inito/RRKM calculations. The number of reaction steps to $C_7{H_7}^+$ is counted for each path. Of the three isomers, the meta mostly goes through the coupling, whereas the para proceeds with little or no coupling. In the beginning, some reactants with high internal energy decay fast to the benzylium ion without any coupling and others rearrange to the other isomers. Later on all three isomers dissociate to the products via long-lived intermediates. Thus, the reactant shows a multiexponential decay and the branching ratio varies with time as the average internal energy decreases with time. The reciprocal of the effective lifetime is taken as the rate constant. The resulting rate-energy curves are in line with experiments. The present results suggest that the coupling between the stable isomers is thermodynamically controlled, whereas the branching to the product is kinetically controlled.