Effect of ammonia and water molecule on OH+CH3OH reaction under tropospheric condition

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 (8.8x10(-13) cm(3) molecule(-1) s(-1)), for OH+CH3OH (+NH3) [1.9x10(-21) cm(3) molecule(-1) s(-1)] and for OH+CH3OH (+H2O) [8.1x10(-16) cm(3) 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.

Automated summary

The study calculated rate coefficients for OH+CH3OH and OH+CH3OH (+X) (X=NH3, H2O) reactions using CVT theory, showing that hydrogen atom abstraction at the CH3 position dominates in both free and catalyzed reactions. The rate coefficients for reactions with NH3 and H2O were found to be significantly smaller than the free reaction. The catalytic effect of a single ammonia or water molecule on the OH+CH3OH reaction is predicted to have no effect under tropospheric conditions.