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

The rate coefficients for OH + CHOH and OH + CHOH (+ X) (X = NH, HO) 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 + CHOH is dominated by the hydrogen atoms abstraction from CH 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 + CHOH (8.8 × 10 cm molecule s), for OH + CHOH (+ NH) [1.9 × 10 cm molecule s] and for OH + CHOH (+ HO) [8.1 × 10 cm molecule s] at 300 K. The rate coefficient is at least 8 order magnitude [for OH + CHOH(+ NH) reaction] and 3 orders magnitude [OH + CHOH (+ HO)] are smaller than free OH + CHOH reaction. Our calculations predict that the catalytic effect of single ammonia and water molecule on OH + CHOH 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.