Atmospheric Chemistry of CH₂OO: The Hydrolysis of CH₂OO in Small Clusters of Sulfuric Acid

Abstract

The hydrolysis of CH2OO is not only a dominant sink for the CH2OO intermediate in the atmosphere but also a key process in the formation of aerosols. Herein, the reaction mechanism and kinetics for the hydrolysis of CH2OO catalyzed by the precursors of atmospheric aerosols, including H2SO4, H2SO4···H2O, and (H2SO4)2, have been studied theoretically at the CCSD­(T)-F12a/cc-pVDZ-F12//B3LYP/6-311+G­(2df,2pd) 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 HOCH2OOH is more strongly bonded to the three catalysts than to the reactants CH2OO and H2O, revealing that small clusters of sulfuric acid promote the hydrolysis of CH2OO both kinetically and thermodynamically. Kinetic simulations show that the H2SO4-assisted reaction is more favorable than the H2SO4···H2O- (the pseudo-first-order rate constant being 27.9–11.5 times larger) and (H2SO4)2- (between 2.8 × 104 and 3.4 × 105 times larger) catalyzed reactions. Additionally, due to relatively lower concentration of H2SO4, the hydrolysis of CH2OO with H2SO4 cannot compete with the CH2OO + H2O or (H2O)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.

Possible atmospheric source of NH2SO3H: the hydrolysis of HNSO2 in the presence of neutral, basic, and acidic catalysts

“…From an energy point of view, the binding energy of t-H 2 SO 4 Á Á ÁH 2 O was 10.4 kcal mol À1 , which agreed well with the previous reported value 28,33,34 of 10.1 kcal mol À1 . Starting from the HNSO 2 + t-H 2 SO 4 Á Á ÁH 2 O reactants, the stepwise route of Channel SA was initiated by complex IM_SA 0 , where a van der Waals interaction (2.60 Å) was formed between the O atom of the H 2 O moiety in t-H 2 SO 4 Á Á ÁH 2 O and the S atom of HNSO 2 .…”

“…The values in brackets are from experiments. 10,11,21,28,29,33,34,[58][59][60][61][62][63] lengths (Å) and bond angles. [58][59][60][61][62][63] The mean absolute deviation of bond lengths (Å) and bond angles (1) between the calculations at the M06-2X/6-311+G(2df,2pd) level and the experimental values were less than 0.01 Å and 1.61, respectively.…”

“…These geometrical structures were also in good agreement with earlier findings. 21,28,29,33,34,65 The stabilization energies of (…”

“…with respect to the isolated reactants were in the range of À2.5 to À18.3 kcal mol À1 , and these energy values matched well with the earlier findings. 11,19,21,28,29,33,34,66 As for the reactant complexes HNSO 2 Á Á ÁH 2 OÁ Á ÁX, their optimized geometries and stabilization energies are illustrated in Fig. 2.…”

“…At the same time, previous studies [30][31][32] have shown that the bimolecular complexes of H 2 SO 4 Á Á ÁH 2 O and (H 2 SO 4 ) 2 are not only the initial cluster formations of the nucleation process when H 2 SO 4 is involved, but also exist in large quantities in a natural environment. Moreover, these two bimolecular acidic catalysts exhibit obvious catalytic effects in the hydrolysis reactions of COS, 28 SO 2 , 21 CH 2 OO, 33 and N 2 O 4 34 by increasing the stability of the reactant complexes and reducing the reaction energy barriers. These situations stimulated our interest in studying the hydrolysis of HNSO 2 by neutral, basic, and acidic catalysts.…”