Theoretical Study of the Gaseous Hydrolysis of NO in the Presence of Amines.

The effects on the hydrolysis of NO in the presence of methylamine and dimethylamine molecules were investigated by theoretical calculations of a series of the molecular clusters 2NO-mHO-CHNH (m = 1-3) and 2NO-mHO-(CH)NH (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 NO 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 (CHNHNO). In addition, the interactions of CHNH and (CH)NH on the hydration of HNO are also more effective than NH, and the NHNO, CHNHNO, and (CH)NHNO complexes tend to form the larger aerosols with the increasing of water molecules. The equilibrium geometries, harmonic vibrational frequencies, and intensities of both HONO-CHNH and HONO-NH complexes were investigated. Calculations predict that the binding energies of both HONO-CHNH complexes are larger than HONO-NH 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 2NO + HO + CHNH and 2NO + HO + (CH)NH, as well as the complexes of HONO-NH and HONO-CHNH. The results show that the interactions with amines are relatively larger, and the higher stabilization energies between CHNH and HONO are found.