Articles | Volume 12, issue 8
Atmos. Chem. Phys., 12, 3591–3599, 2012
https://doi.org/10.5194/acp-12-3591-2012
Atmos. Chem. Phys., 12, 3591–3599, 2012
https://doi.org/10.5194/acp-12-3591-2012

Research article 16 Apr 2012

Research article | 16 Apr 2012

Amine substitution into sulfuric acid – ammonia clusters

O. Kupiainen1, I. K. Ortega1, T. Kurtén2, and H. Vehkamäki1 O. Kupiainen et al.
  • 1Division of Atmospheric Sciences, Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland
  • 2Laboratory of Physical Chemistry, Department of Chemistry, P.O. Box 55, 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.

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