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Atmos. Chem. Phys. Discuss., 11, 30853-30875, 2011
www.atmos-chem-phys-discuss.net/11/30853/2011/ doi:10.5194/acpd-11-30853-2011 © Author(s) 2011. This work is distributed under the Creative Commons Attribution 3.0 License. |
Amine substitution into sulfuric acid – ammonia clusters
Division of Atmospheric Sciences, Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland
Abstract. The substitution of ammonia by dimethylamine in sulfuric acid – ammonia – dimethylamine clusters was studied using a collision and evaporation dynamics model. Quantum chemical formation free energies were computed using B3LYP/CBSB7 for geometries and frequencies and RI-CC2/aug-cc-pV(T+d)Z for electronic energies. We first demonstrate the good performance of our method by a comparison with an experimental study investigating base substitution in positively charged clusters, and then continue by simulating base exchange in neutral clusters, which cannot be measured directly. Collisions of a dimethylamine molecule with an ammonia containing positively charged cluster result in the instantaneous evaporation of an ammonia molecule, while the dimethylamine molecule remains in the cluster. According to our simulations, a similar base exchange can take place in neutral clusters, although the overall process is more complicated. Neutral sulfuric acid – ammonia clusters are significantly less stable than their positively charged counterparts, resulting in a competition between cluster evaporation and base exchange.
Citation: Kupiainen, O., Ortega, I. K., Kurtén, T., and Vehkamäki, H.: Amine substitution into sulfuric acid – ammonia clusters, Atmos. Chem. Phys. Discuss., 11, 30853-30875, doi:10.5194/acpd-11-30853-2011, 2011.