Toward elimination of discrepancies between theory and experiment: The rate constant of the atmospheric conversion of SO3 to H2SO4

• Published in: Proceedings of the National Academy of Sciences - PNAS 2000-08, Vol.97 (16), p.8874-8878
• Main Authors: Loerting, T, Liedl, K R
• Format: Article
• Language: English
• Subjects: Atmosphere; Chemistry; Molecules; Physical Sciences; Protons
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.97.16.8874

The hydration rate constant of sulfur trioxide to sulfuric acid is shown to depend sensitively on water vapor pressure. In the 1:1 SO 3 -H 2 O complex, the rate is predicted to be slower by about 25 orders of magnitude compared with laboratory results [Lovejoy, E. R., Hanson, D. R. & Huey, L. G. (1996) J. Phys. Chem. 100, 19911–19916; Jayne, J. T., Pöschl, U., Chen, Y.-m., Dai, D., Molina, L. T., Worsnop, D. R., Kolb, C. E. & Molina, M. J. (1997) J. Phys. Chem. A 101, 10000–10011]. This discrepancy is removed mostly by allowing a second and third water molecule to participate. An asynchronous water-mediated double proton transfer concerted with the nucleophilic attack and a double proton transfer accompanied by a transient H 3 O + rotation are predicted to be the fastest reaction mechanisms. Comparison of the predicted negative apparent “activation” energies with the experimental finding indicates that in our atmosphere, different reaction paths involving two and three water molecules are taken in the process of forming sulfate aerosols and consequently acid rain.