The energetics and kinetics of the CH3CHO + (CH3)2NH/CH3NH2 reactions catalyzed by a single water molecule in the atmosphere

We have used quantum chemical methods and transition state theory with Eckart tunneling to study the water-catalyzed addition reaction of dimethylamine ((CH3)(2)NH) and methylamine (CH3NH2) with acetaldehyde (CH3CHO) responsible for the formation of organic amines acted as the important precursors in the atmospheric nucleation processes. The calculated results show that the CH3CHO + (CH3)(2)NH reaction is more feasible than the CH3CHO + CH3NH2 reaction because the energy barrier of the CH3CHO + (CH3)(2)NH reaction is about 3 kcal/mol lower than that of the CH3CHO + CH3NH2 reaction. In addition, a single water molecule can substantially reduce the energy barriers of the CH3CHO + (CH3)(2)NH/CH(3)NH(2 )reactions. In particular, the reaction barrier of CH3CHO + (CH3)(2)NH is decreased from 23.46 to -1.3 kcal/mol with a single water molecule involved. The calculated rate constants also show that the CH3CHO + (CH3)(2)NH + H2O reaction has strong negative temperature dependence and is about 10 orders of magnitude faster than CH3CHO + (CH3)(2)NH. Our results suggest that the CH3CHO + (CH3)(2)NH + H2O reaction could make a non-negligible contribution to the aerosol nucleation under some atmospheric conditions.