Effect of ammonia and water molecule on OH + CH3OH reaction under tropospheric condition
Mohamad Akbar Ali, M. Balaganesh, Faisal Al‐Odail, King‐Chuen Lin
Abstract
Abstract The rate coefficients for OH + CH 3 OH and OH + CH 3 OH (+ X) (X = NH 3 , H 2 O) 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 + CH 3 OH is dominated by the hydrogen atoms abstraction from CH 3 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 + CH 3 OH (8.8 × 10 −13 cm 3 molecule −1 s −1 ), for OH + CH 3 OH (+ NH 3 ) [1.9 × 10 −21 cm 3 molecule −1 s −1 ] and for OH + CH 3 OH (+ H 2 O) [8.1 × 10 −16 cm 3 molecule −1 s −1 ] at 300 K. The rate coefficient is at least 8 order magnitude [for OH + CH 3 OH(+ NH 3 ) reaction] and 3 orders magnitude [OH + CH 3 OH (+ H 2 O)] are smaller than free OH + CH 3 OH reaction. Our calculations predict that the catalytic effect of single ammonia and water molecule on OH + CH 3 OH 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.