Theoretical Study Of The Gaseous Hydrolysis Of NO₂ In The Presence Of Methylamine And Dimethylamine

Nitrous acid?HONO?and nitrogen-containing particulate matter are two typical pollutants in atmospheric chemistry and air pollution,and they are inseparable.Nitrous acid has been recognized as an important trace gas in the troposphere,it could rapidly undergoes photolysis by sunlight to release a significant amount of hydroxyl?OH?radicals.The sources and the chemical mechanisms of HONO are not well understood despite its importance are well recognized.The effects on the hydrolysis of NO₂ in the presence of methylamine and dimethylamine molecules have been 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?and compared with ammonia.The reactions are as followed:2NO₂?g?+ mH₂O?g?+ CH₃NH₂?g??products?m=1-3?2NO₂?g?+ mH₂O?g?+?CH₃?₂NH?g??products?m=1,2?The results show that methylamine and dimethylamine 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 promoting to form the methylamine nitrate.With methylamine included in the clusters,the energy barrier is reduced by 3.2 kcal/mol,and the corresponding products are more stable.In addition,the effects of CH₃NH₂ and?CH₃?₂NH on the hydration of HNO3 are also more effectively than NH₃,and the NH4NO3,CH₃NH₃NO3 and?CH₃?₂NH₂NO3 complexes tend to form the larger aerosols with the additional of water molecules.The equilibrium geometries,harmonic vibrational frequencies and intensities of both HONO-CH₃NH₂ and HONO-NH₃ complexes have been 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?NBO?analysis has been carried out to describe the donor-acceptor interactions on a series of complexes in the reactions.The results show that the interactions with methylamine and dimethylamine are relatively larger than that of ammonia,and the higher stabilization energies between CH₃NH₂ and HONO are found.