Prof. Christopher Johnson
Prof. Christopher Johnson
Department of Chemistry
Stony Brook University
Chemistry Building, Room 400
Physical Seminar

New particle formation (NPF) is the process by which trace atmospheric gases cluster and grow into small particles.  These particles make up a substantial fraction of climatically-relevant aerosols, but they are difficult to study due to their small size and ephemeral nature.  We are particularly interested in the role of intermolecular interactions such as proton transfer and hydrogen bonding in governing particle formation and growth.  Our group has been using vibrational spectroscopy and temperature-controlled ion trap mass spectrometry to evaluate the structures, energetics, and growth of clusters of sulfuric acid with ammonia and amines, the species predicted to dominate the early stages of growth.  Hydrogen bonding and Coulombic interactions between conjugate acid and base ions show an interesting interplay in determining the cluster structure.  We have also examined the hydration of these clusters, an elusive factor in the overall NPF mechanism due to difficulties in unambiguously detecting hydration using sampling techniques.  The uptake of water in our experiments correlates strongly to the number of hydrogen bond donors on the surface of the cluster, and more weakly with the net basicity of the cluster.  In fact, the correlation with basicity is no stronger than the correlation between basicity and number of hydrogen bond donors.  This suggests that, contrary to earlier expectations, structure is the dominant factor in determining the hydration of these new particles