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
Received: 15 Sep 2011 – Published in Atmos. Chem. Phys. Discuss.: 18 Nov 2011
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.
Revised: 23 Mar 2012 – Accepted: 30 Mar 2012 – Published: 16 Apr 2012
Kupiainen, O., Ortega, I. K., Kurtén, T., and Vehkamäki, H.: Amine substitution into sulfuric acid – ammonia clusters, Atmos. Chem. Phys., 12, 3591-3599, doi:10.5194/acp-12-3591-2012, 2012.