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Laser photolysis/laser‐induced fluorescence studies of reaction rates of OH with CH 3 Cl, CH 2 Cl 2 , and CHCl 3 over an extended temperature range
Author(s) -
Taylor Philip H.,
D'angelo Joe A.,
Martin Marc C.,
Kasner James H.,
Dellinger Barry
Publication year - 1989
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550210908
Subject(s) - chemistry , arrhenius equation , atmospheric temperature range , exponent , reaction rate constant , flash photolysis , photodissociation , radical , thermodynamics , range (aeronautics) , activation energy , analytical chemistry (journal) , photochemistry , kinetics , organic chemistry , quantum mechanics , composite material , linguistics , physics , philosophy , materials science
A modified laser photolysis/laser‐induced fluorescence technique has been used to measure atmospheric pressure absolute rate coefficients for the reaction of hydroxyl (OH) radicals with the chlorinated methanes (CH 3 Cl, CH 2 Cl 2 , and CHCl 3 ). Data have been obtained for these compounds over the widest temperature range (292–800 K) that has been reported in the literature using a single experimental apparatus. The temperature dependence of the rate data is best represented by the following three‐parameter expressions:\documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}_{\rm 3} {\rm Cl:}\,{\rm 8}{\rm .38}\,\, \pm \,\,1.07\,\, \times \,\,10^{ - 16} \,{\rm T}^{{\rm 1}{\rm .38} \pm {\rm 2}{\rm .01/0}{\rm .71}} \exp [- 2387.4\,\, \pm \,\,142.8/RT]({\rm cm}^3 /{\rm molec - s)}$$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}_{\rm 2} {\rm Cl}_{\rm 2} {\rm :}\,\,1.{\rm 52}\,\, \pm \,\,0.16\,\, \times \,\,10^{ - 16} \,{\rm T}^{{\rm 1}{\rm .58} \pm 0.45} \exp [- 1236.3\,\, \pm \,\,119.5/RT]({\rm cm}^3 /{\rm molec - s)}$$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$${\rm CHCl}_{\rm 3} {\rm :}\,\,1.{\rm 92}\,\, \pm \,\,0.21\,\, \times \,\,10^{ - 20} \,{\rm T}^{{\rm 2}{\rm .78} \pm 0.34/0.42} \exp [- 188.3\,\, \pm \,\,119.3/RT]({\rm cm}^3 /{\rm molec-s)}$$\end{document} Uncertainties in the pre‐exponential and exponential term are expressed as 95% confidence intervals. For the temperature exponent, error limits represent a ±10% change in the total error of best fit. The degree of curvature in the Arrhenius plots appeared to increase with increasing Cl substitution of the reactant. However, the uncertainty in the temperature exponent for the CH 3 Cl data was large in comparison with the other chlorinated methanes. Thus, data of greater precision at elevated temperatures are necessary to further explore this relationship. The rate coefficients were compared with recent semiempirical and transition state theory models for haloalkane‐OH hydrogen transfer reactions over a temperature range of 250–800 K. The transition state model of Cohen and Benson was in excellent agreement with the CH 3 Cl and CH 2 Cl 2 data. The semiempirical structure activity relationship developed by Atkinson represented the best fit of the CHCl 3 data, although it underestimated the experimental data by more than a factor of 2 at 800 K. The extreme care used to remove and alayze for reactive impurities along with the agreement with other experimental studies suggests that transition state and semi‐empirical models for CHCl 3 must be modified to account its reaction behavior at high temperature.