New mechanistic pathways for organosulfates formation catalyzed by ammonia and carbinolamine formation catalyzed by sulfuric acid in the atmosphere
In the secondary organic aerosol formation, exploring the formation of nucleation precursors is of paramount important for understanding secondary organic aerosol formation. Here, we report new mechanistic pathways for organosulfates and carbinolamine formation in the atmospheric gas phase by utilizing high-level W2X//QCISD/cc-pV(T+d)Z method close to CCSD(T)/CBS accuracy, dual level kinetics strategy by combining multistructural variational transition state theory with small-curvature tunneling at the M08-SO/maug-cc-pVTZ level with conventional transition state theory at the W2X//QCISD/cc-pV(T+d)Z level, and torsional anharmonicity. However, the previously suggested mechanism indicated that they are only formed in the heterogeneous atmospheric chemical processes. Furthermore, we find that ammonia only exerts a catalytic role in the HCHO + H2SO4 reaction responsible for the formation of organosulfate under some atmospheric conditions, whereas sulfuric acid can significantly promote the HCHO + NH3 reactions, resulting in the formation of carbinolamine in the atmosphere. These present results also show that the ammonia-catalyzed reaction of formaldehyde with sulfuric acid can play an important role in the sink of formaldehyde and the sulfuric acid-catalyzed reaction of formaldehyde with ammonia can also make contribution to the sink of ammonia under some atmospheric conditions. In theory, the detailedly computational strategies have been designed to obtain quantitative rate constants for these reactions investigated here. Additionally, the calculated results show that M08-SO functional can provide reliable results for describing the reactions investigated here with unsigned error bars of less than 1 kcal/mol. The recrossing effects remarkably decrease the rate constant of the reaction between HCHO and H2SO4NH3.