This title appears in the Scientific Report :
2014
Please use the identifier:
http://dx.doi.org/10.1039/C4CP02073A in citations.
Reversible addition of the OH radical to p-cymene in the gas phase: multiple adduct formation. Part 2
Reversible addition of the OH radical to p-cymene in the gas phase: multiple adduct formation. Part 2
A flash photolysis-resonance fluorescence (FP-RF) system was used to study the p-cymene (PC) + OHreaction at temperatures between 299 and 349 K in helium. Triexponential functions were fitted to groups ofobserved OH decay curves according to a model considering a reversible addition to form two addu...
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Personal Name(s): | Alarcón, Paulo (Corresponding Author) |
---|---|
Bohn, Birger / Zetzsch, Cornelius / Rayez, Marie-Thérèse / Rayez, Jean-Claude | |
Contributing Institute: |
Troposphäre; IEK-8 |
Published in: | Physical chemistry, chemical physics, 16 (2014) S. 17315-17326 |
Imprint: |
Cambridge
RSC Publ.
2014
|
DOI: |
10.1039/C4CP02073A |
Document Type: |
Journal Article |
Research Program: |
Trace gas and aerosol processes in the troposphere |
Publikationsportal JuSER |
A flash photolysis-resonance fluorescence (FP-RF) system was used to study the p-cymene (PC) + OHreaction at temperatures between 299 and 349 K in helium. Triexponential functions were fitted to groups ofobserved OH decay curves according to a model considering a reversible addition to form two adducts asthermolabile reservoirs of OH. Compared to Part 1 of this paper, consideration of a second adduct stronglyimproved the fits to our measurements, and the rate constants for the major pathways were optimizedbetween 299 and 349 K. The Arrhenius expression for the rate constant of the sum of OH addition andH-atom abstraction pathways was found to be kOH = 1.9 1012 exp[(610 210) K/T] cm3 s1. Rateconstants of unimolecular decomposition reactions of the adducts were similar to other aromaticcompounds with the following Arrhenius expressions: 1 1012 exp[(7600 800) K/T] s1 for adduct1 and 4 1011 exp[(8000 300) K/T] s1 for adduct 2. Adduct yields increased and decreased withtemperature for adduct 1 and 2, respectively, but were similar (B0.4) around room temperature.Equilibrium constants yielded values for reaction enthalpies and entropies of adduct formations. Whilefor one adduct reasonable agreement was obtained with theoretical predictions, there were significantdeviations for the other adduct. This indicates the presence of more than two adduct isomers that werenot accounted for in the reaction model. Quantum chemical calculations (DFT M06-2X/6-31G(d,p)) andRRKM kinetics were employed with the aim of clarifying the mechanism of the OH addition to PC.These calculations show that formation of adducts with OH in ortho positions to the isopropyl andmethyl substituents is predominant (55% and 24%) to those with OH in ipso positions (21% and 3%).A large fraction (490%) of the ipso-C3H7 adduct is predicted to react by dealkylation forming p-cresol(in the absence of oxygen) and isopropyl radicals. These theoretical results agree well with the interpretationof the experimental results showing that the two ortho adducts (which appeared as OHreservoirs in the experiment) have been observed. |