Articles | Volume 12, issue 8
https://doi.org/10.5194/acp-12-3591-2012
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. Kupiainen, I. K. Ortega, T. Kurtén, and H. Vehkamäki

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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