Effect of ammonia and water molecule on OH\u2009+\u2009CH3OH reaction under tropospheric condition

Abstract

The rate coefficients for OH\u2009+\u2009CH3OH and OH\u2009+\u2009CH3OH (+\u2009X) (X\u2009=\u2009NH3, 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\u2009+\u2009CH3OH 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\u2009+\u2009CH3OH (8.8\u2009×\u200910−13 cm3 molecule−1 s−1), for OH\u2009+\u2009CH3OH (+\u2009NH3) [1.9\u2009×\u200910−21 cm3 molecule−1 s−1] and for OH\u2009+\u2009CH3OH (+\u2009H2O) [8.1\u2009×\u200910−16 cm3 molecule−1 s−1] at 300 K. The rate coefficient is at least 8 order magnitude [for OH\u2009+\u2009CH3OH(+\u2009NH3) reaction] and 3 orders magnitude [OH\u2009+\u2009CH3OH (+\u2009H2O)] are smaller than free OH\u2009+\u2009CH3OH reaction. Our calculations predict that the catalytic effect of single ammonia and water molecule on OH\u2009+\u2009CH3OH 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.