Trifluoroacetaldehyde aminolysis catalyzed by a single water molecule: An important sink pathway for trifluoroacetaldehyde and a potential pathway for secondary organic aerosol growth

Abstract

High-level ab initio calculations and variational transition state theory with small curvature tunneling have been used to study the aminolysis of trifluoroacetaldehyde catalyzed by a single water molecule. The results of energetic studies indicate that the energy barrier of the trifluoroacetaldehyde aminolysis reaction decreases along ammonia, methylamine, and dimethylamine. A single water molecule can significantly reduce the reaction energy barrier of trifluoroacetaldehyde aminolysis. In particular, the reaction involving dimethylamine has the lowest reaction energy barrier and the energy barrier is decreased to be −9.69 kcal/mol in the CF3CHO + (CH3)2NH + H2O reaction relative to CF3CHO, (CH3)2NH, and H2O separated reactants. Kinetic calculation shows that the rate coefficient of CF3CHO + (CH3)2NH⋯H2O ranges from 7.78 × 10−13 to 4.45 × 10−16 cm3⋅molecules−1⋅s−1 at 190–350 K. Here, we find an important CF3CHO elimination pathway, which can compete with the reaction of CF3CHO + OH when the OH concentration is 104 molecules⋅cm−3 and the dimethylamine concentration is higher than 109 molecules⋅cm−3 in the temperature range between 240 and 330 K. In addition, once (CH3)2NCH(OH)CF3 is formed by the reaction of CF3CHO + (CH3)2NH + H2O, it will further promote the growth of secondary organic aerosols.