Journal Article

PreJuSER-22983

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Kinetics and mechanism of the reaction of OH with the trimethlbenzenes - experimental evidence for the formation of adduct isomers

Bohn, B.FZJ* ; Zetzsch, C.

2012
RSC Publ. Cambridge

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Please use a persistent id in citations: http://hdl.handle.net/2128/7596  doi:10.1039/C2CP42434G

Abstract: The reversible gas-phase addition of OH radicals to the trimethylbenzenes was investigated in pulsed experiments utilizing VUV flash-photolysis resonance-fluorescence of H(2)O in the temperature range of 275-340 K. Triexponential OH decays were observed in the presence of the trimethylbenzenes, indicating the participation of more than one adduct species. Analytical solutions for the system of differential equations with two adduct isomers were derived, and the OH decay curves were evaluated based on this reaction model. This led to significant improvements of fit qualities and notable changes in OH rate constants compared to a previous model with a single adduct species. The detailed analysis was confined to 1,3,5-trimethylbenzene where reversible formation of two OH-aromatic ortho- and ipso-adduct isomers is feasible in accordance with the extended reaction model. Only after inclusion of additional isomerization reactions, consistent thermochemical data were obtained from the fitted rate constants. Reaction enthalpies of -83 ± 7 kJ mol(-1) and -35 ± 22 kJ mol(-1) were derived for the formation of one adduct isomer and the isomerization into the other, respectively. Based on literature data, the more and less stable adducts were assigned to ipso- and ortho-adduct isomers, respectively. The potential isomerization precluded the determination of primary yields of adduct isomers but formation of the ipso-adduct in any case is a minor process. For the rate constants of the OH + 1,3,5-trimethylbenzene reaction an Arrhenius expression k(OH) = 1.32 × 10(-11) cm(3) s(-1) exp(450 ± 50 K/T) was obtained. Based on the same approach, the rate constants of the OH reactions with 1,2,3-trimethylbenzene and 1,2,4-trimethylbenzene were derived as k(OH) = 3.61 × 10(-12) cm(3) s(-1) exp(620 ± 80 K/T) and k(OH) = 2.73 × 10(-12) cm(3) s(-1) exp(730 ± 70 K/T), respectively.

Keyword(s): J

Note: This work was supported within the joint French-German research project ATMOCHEM funded by the Deutsche Forschungsgemeinschaft under grant BO-1580/3-1 and ZE 792/6-1. We thank R. Koch for detecting the triexponential feature of the decays of OH in the presence of 1,3,5-trimethylbenzene, M. Elend for the GC-analysis of the liquid reactants, and R. Koch and M. Siese for their efforts to improve the instrument.

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Contributing Institute(s):

1. Troposphäre (IEK-8)

Research Program(s):

1. Atmosphäre und Klima (P23)

Appears in the scientific report 2012

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Database coverage:
; ; Allianz-Lizenz / DFG ; Current Contents - Social and Behavioral Sciences ; JCR ; NCBI Molecular Biology Database ; Nationallizenz ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Thomson Reuters Master Journal List ; Web of Science Core Collection

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