Atmospheric Chemistry of CH 2 OO: The Hydrolysis of CH 2 OO in Small Clusters of Sulfuric Acid.

The hydrolysis of CH ₂ OO is not only a dominant sink for the CH ₂ OO intermediate in the atmosphere but also a key process in the formation of aerosols. Herein, the reaction mechanism and kinetics for the hydrolysis of CH ₂ OO catalyzed by the precursors of atmospheric aerosols, including H ₂ SO ₄ , H ₂ SO ₄ ···H ₂ O, and (H ₂ SO ₄ ) ₂ , have been studied theoretically at the CCSD(T)-F12a/cc-pVDZ-F12//B3LYP/6-311+G(2 df ,2 pd ) level. The calculated results show that the three catalysts decrease the energy barrier by over 10.3 kcal·mol ^-1 ; at the same time, the product formation of HOCH ₂ OOH is more strongly bonded to the three catalysts than to the reactants CH ₂ OO and H ₂ O, revealing that small clusters of sulfuric acid promote the hydrolysis of CH ₂ OO both kinetically and thermodynamically. Kinetic simulations show that the H ₂ SO ₄ -assisted reaction is more favorable than the H ₂ SO ₄ ···H ₂ O- (the pseudo-first-order rate constant being 27.9-11.5 times larger) and (H ₂ SO ₄ ) ₂ - (between 2.8 × 10 ⁴ and 3.4 × 10 ⁵ times larger) catalyzed reactions. Additionally, due to relatively lower concentration of H ₂ SO ₄ , the hydrolysis of CH ₂ OO with H ₂ SO ₄ cannot compete with the CH ₂ OO + H ₂ O or (H ₂ O) ₂ reaction within the temperature range of 280-320 K, since its pseudo-first-order rate ratio is smaller by 4-7 or 6-8 orders of magnitude, respectively. However, the present results provide a good example of how small clusters of sulfuric acid catalyze the hydrolysis of an important atmospheric species.