Abstract
The rate coefficients for OH + CH3OH and OH + CH3OH (+ X) (X = NH3, H2O) reactions were calculated using microcanonical, and canonical variational transition state theory (CVT) between 200 and 400 K based on potential energy surface constructed using CCSD(T)//M06-2X/6-311++G(3df,3pd). The results show that OH + CH3OH is dominated by the hydrogen atoms abstraction from CH3 position in both free and ammonia/water catalyzed ones. This result is in consistent with previous experimental and theoretical studies. The calculated rate coefficient for the OH + CH3OH (8.8 × 10−13 cm3 molecule−1 s−1), for OH + CH3OH (+ NH3) [1.9 × 10−21 cm3 molecule−1 s−1] and for OH + CH3OH (+ H2O) [8.1 × 10−16 cm3 molecule−1 s−1] at 300 K. The rate coefficient is at least 8 order magnitude [for OH + CH3OH(+ NH3) reaction] and 3 orders magnitude [OH + CH3OH (+ H2O)] are smaller than free OH + CH3OH reaction. Our calculations predict that the catalytic effect of single ammonia and water molecule on OH + CH3OH reaction has no effect under tropospheric conditions because the dominated ammonia and water-assisted reaction depends on ammonia and water concentration, respectively. As a result, the total effective reaction rate coefficients are smaller. The current study provides a comprehensive example of how basic and neutral catalysts effect the most important atmospheric prototype alcohol reactions.
Highlights
The rate coefficients for OH + C H3OH and OH + C H3OH (+ X) (X = N H3, HO → CH2OH + (H2O)) reactions were calculated using microcanonical, and canonical variational transition state theory (CVT) between 200 and 400 K based on potential energy surface constructed using CCSD(T)//M06-2X/6-311++G(3df,3pd)
To abstract the hydrogen atom from CH3 and OH group, OH of R C1 rotate in the plane until O atom come closer to the C H3 and OH group of CH3OH to pass via the geometry of T Sa and T Sb
The rate coefficients for two important reaction pathways OH + C H3OH···X (X = H2O, NH3) and CH3OH + HO···X (X = H 2O, NH3) were computed calculated using CCSD(T)/6-311++G(3df,2p)//M062X/6-311++G(3df,2p) level with CVT/SCT approach and results were compared with previously published data
Summary
The results show that OH + C H3OH is dominated by the hydrogen atoms abstraction from CH3 position in both free and ammonia/water catalyzed ones This result is in consistent with previous experimental and theoretical studies. Nguyen et al.[5] reported reaction rate coefficients for OH + C H3OH reaction at temperature ≤ 200 K They suggested that the formation of C H3O radical plays a more important role due to quantum mechanical tunneling. To the best of our knowledge, there is only one theoretical study reported by Jonas et al on the catalytic effect of NH3 on the OH + C H3OH reaction[9] They have investigated the mechanism and kinetics of the OH + C H3OH reaction with and without the presence of H2O, NH3, and H2SO4 using ab initio/DFT.
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