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MULTI-REACTIONAL MULTICONFORMATIONAL KINETIC STUDY OF ETHIL VINYL ETHER (EVE) + OH REACTION
Vinícius Nunes da Rocha
Universidade Federal Rural do Rio de Janeiro
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Create a topic1. Aliphatic ethers have been suggested as fuel addictive, quoted to change the energetic matrix;
2.This study focuses on the EVE + OH reaction, describing its global reaction kinetics;
3. Calculations have been done at M06-2x level with the aug-cc-pVTZ basis utilizing the ORCA software;
4. The complete reaction mechanism including all conformations was proposed;
5. Corrections for the Morse Oscillator and Wigner Tunneling were included in the rate coefficients;
6. Rate coefficients were calculated in a vast temperature range of 200 – 2500K.
Mateus Quintano
Hi, Vinícius! Congratulations on your excellent work! Just for the sake of curiosity:
1) How would you explain such an impressive agreement with experiment at the single-reference level of theory? Correct me if I am wrong, but the intermediate species are in doublet states, aren't they?
2) Also, do the OH-initiated intermediates undergo further unimolecular decomposition? If so, do they obey the Lindemann Mechanism? If not, would the fast-equilibrium approximation apply? Could you please clarify that? Thank you!
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Vinícius Nunes da Rocha
Good morning, Mateus. Thank you for the complements and interest in our work, for these great questions and your time! Well, let me answer in parts as you did questioning:
1) This impressive agreement, even at single-level of theory can be explained mostly by the detailment of theoretical model that we built for the EVE + OH reaction. The connectivity between these chemical species plays an important role to reproduce the qualitative behavior of the reaction at a first glance ( non-Ahrrenius behavior at 230 - 350 K temperature range, shown by the experimental data) and the meticulous kinect study based on this model and its particularities naturaly could be reproduced. Even though the direct and reverse kinect coefficients from post-barrier intermediates to products are negligible to this model, the connectivity between the transition states and those post-barriers intermediates plays an important role to fit the experimental data to the curve. Nevertheless, the Ahrrenius curve presented receive mainly the contribution from addition channels at low temperatures.
This can explain also the better agreement when we compare this model with literature theoretical work from before. The calculated energy barries based on this connectivity proposed could explain the most viable and not viable hydrogen abstraction and OH addition channels, well know by literature as well.
Furthermore, this single-referenced level of theory is fundamented by previous works in our laboratory and even by literature in a variety of similar chemical space case scenarious (a bunch of OH radical reactions with aliphatic ethers, hydrocarbonates, aldehydes and esters). This functional can generate energies close to the CCSDT level of theory within less computational cost. The multiconfigurational nature are measured by T1 parameter and we followed the <S^2> autovalues. Finally, yes, you are correct, these species are at doublet state!
2) Yes. This theoretical model considered 400 K as intermediates decomposition temperature limit. Above that temperature, the reaction adopts a direct reaction behavior from reactants to the products. This can be confirmed by variational transition state theory calculations, following the s coordinate. Before that we have to consider all the possiblie paths within intermediates participation and its population.
Hope I could sanate your doubts about our work. If not, please don't be shy to question and ponctuate anything! It will be a pleasure to answer!
Thanks!