David A. Hales

Professor of Chemistry and Chair, Department of Chemistry

Ph.D., University of California-Berkeley

Research interest: Ionized molecules and their reactions

Ionized molecules and their reactions play an important role in many environments, including our atmosphere and some industrial processes, such as plasma processing of semiconductors and certain polymer-forming reactions. In order to study such processes, we examine reactions of ions within small clusters of molecules in the gas phase. The clusters are generated in high vacuum, so that they are isolated from each other and from other chemical species. Once formed, they are ionized by removal of an electron, and then the resulting cluster ions are analyzed by mass spectrometry. We can select individual cluster masses and examine their fragmentation to help us determine where reactions within the cluster ion have formed new covalent bonds or broken old ones. The experimental techniques used in this work include adiabatic expansion, laser photoionization, laser photodissociation, and time-of-flight mass spectrometry.

Determination of the masses of the various clusters that are produced reveals their chemical compositions. Once we know the chemical make-up of the various cluster ions, we use computational quantum chemistry software to model their structures. The calculated structures are compared to the results from our fragmentation experiments, which helps us see whether the predicted structures make sense in light of the experimentally observed fragmentation patterns, and vice versa.