AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Structure and Energetics of Uncharged Sulfuric Acid Clusters with Ammonia and Amines
JOSEPH DEPALMA, Douglas Doren, Murray Johnston, University of Delaware
Abstract Number: 375 Working Group: Aerosol Nucleation: From Clusters to Nanoparticles
Abstract Experimental and computational work has suggested amine substitution occurs favorably into charged ammonium bisulfate clusters of either polarity, implicating amines as a potential channel for new particle formation and growth. The energetics of amine substitution has been explained by a combination of cluster structural features, binding energies, and molecular gas phase basicity (DePalma et al., J. Phys. Chem., 2012). Yet in the atmosphere, the majority of clusters are uncharged. Uncharged clusters are more difficult to study experimentally, making computation an indispensible tool for characterization. The work to be presented here examines the structure, energetics, and reactivity of uncharged clusters of sulfuric acid with ammonia and dimethylamine using quantum mechanics. Clusters were studied with both classical numerical sampling and varying levels of quantum chemistry. Preliminary results suggest that uncharged clusters have structural features akin to both positively charged and negatively charged clusters of similar composition, and that these features are size dependent. Cluster binding energies are similar in magnitude to positively charged clusters of similar size. Amine substitution for ammonia appears to be favorable, with values comparable to positively charged clusters. While bisulfate anions are preferentially formed in small clusters, sulfate anions become more prevalent as the cluster size increases. The role of explicit hydration of uncharged clusters and its effect on structure, binding, and amine substitution is also being explored. Computational results will be discussed in the context of likely cluster growth pathways in the atmosphere.