A Density Functional Theory Study of the Hydrates of NH3·H2SO4 and Its Implications for the Formation of New Atmospheric Particles

Density functional molecular orbital theory was used at the B3LYP/ 6-311++G(2d,2p)//B3LYP/6-311++G(2d,2p) level of theory to study the hydrates of NH 3 ·H 2 SO 4 · n H 2 O for n = 0−5 and NH 3 ·(H 2 SO 4 ) 2 ·H 2 O. Neutrals of the first four NH 3 ·H 2 SO 4 · n H 2 O clusters ( n = 0−4) spontaneously formed and were determined to be hydrogen-bonded molecular complexes of H 2 SO 4, H 2 O, and NH 3 . Double ions (clusters containing a NH 4 + cation and a HSO 4 - anion) spontaneously formed in clusters of NH 3 ·H 2 SO 4 · n H 2 O where n = 1−5. The energetics of the hydration and isomerization reactions also were calculated. Double ions are not energetically favorable until NH 3 ·H 2 SO 4 ·4H 2 O. The free energy of formation from free NH 3 and H 2 SO 4 · n H 2 O had a maximum at n = 3 at room temperature with Δ G ≈ −3 kcal/mol. NH 3 ·(H 2 SO 4 ) 2 ·H 2 O was studied to see if NH 3 can initiate new atmospheric particle growth. It has been shown that NH 3 has no role in the initialization of new atmospheric particles.