Theoretical Study of the Gaseous Hydrolysis of NO2 in the Presence of Amines

The effects on the hydrolysis of NO2 in the presence of methylamine and dimethylamine molecules were investigated by theoretical calculations of a series of the molecular clusters 2NO2-mH2O–CH3NH2 (m = 1–3) and 2NO2-mH2O-(CH3)2NH (m = 1, 2). With methylamine included in the clusters, the energy barrier is reduced by 3.2 kcal/mol from that with ammonia, and the corresponding products may form without an energy barrier. The results show that amines have larger effects than ammonia in promoting the hydrolysis of NO2 on thermodynamics. The additional water molecules can stabilize the transition states and the product complexes, and we infer that adding more water molecules in the reactions mainly act as solvent and promoting to form the methylamine nitrate (CH3NH3+NO3–). In addition, the interactions of CH3NH2 and (CH3)2NH on the hydration of HNO3 are also more effective than NH3, and the NH4NO3, CH3NH3NO3, and (CH3)2NH2NO3 complexes tend to form the larger aerosols with the increasing of water molecules. The equilibrium geometries, harmonic vibrational frequencies, and intensities of both HONO–CH3NH2 and HONO–NH3 complexes were investigated. Calculations predict that the binding energies of both HONO–CH3NH2 complexes are larger than HONO–NH3 complexes, and the OH stretching vibrational frequencies and intensities are most affected. The natural bond orbital analysis was performed to describe the donor–acceptor interactions on a series of complexes in the reactions 2NO2 + H2O + CH3NH2 and 2NO2 + H2O + (CH3)2NH, as well as the complexes of HONO–NH3 and HONO–CH3NH2. The results show that the interactions with amines are relatively larger, and the higher stabilization energies between CH3NH2 and HONO are found.