Professor Kenneth Leopold

This work involves the application of microwave spectroscopy to the study of small molecular complexes that are on the brink of chemical change. It provides an interesting venue for studying the interplay between aggregation and chemical reactivity. MSI resources are used to compute binding energies and to obtain structural information that is not readily accessible experimentally. In appropriate cases, the researchers also compute atomic charges and CH₃ internal rotation barriers. The combination of theory and experiment allows them to say more about the systems they study than either would by itself. Calculations done at MSI also allow the researchers to make predictions that aid in searching for and identifying new spectra.

Current work includes experimental and computational studies of a broader set of complexes than the group has studied to date. For example, they have significant interest in the properties of carboxylic sulfuric anhydrides (CSAs), a class of molecules they discovered a few years ago. Previous calculations done at MSI have indicated that the complex formed from acetic sulfuric anhydride (ASA) and ammonia consists of a proton-transferred ion pair, suggesting that ASA is a very strong acid, perhaps a superacid. The researchers would like to perform additional calculations on a number of other carboxylic sulfuric anhydrides to establish the generality of the strong acidity of CSAs and to guide the experimental verification of these predictions. The researchers are also interested pursuing similar calculations involving methanesulfonic acid and some of the selenium analogs of these compounds. Specifically, for SeO₂ and SeO₃, prior calculations done at MSI indicate a facile reaction with carboxylic acids (analogous to the reactions with SO₃) and this is an exciting avenue the group hopes to pursue. This work is at the very beginning and more calculations will likely be needed, both to guide experiments and to augment the interpretation of the results, should the experiments be successful. Finally, the researchers have recently observed the reaction product of SO₃ and thiobenzoic acid in the laboratory, which reprents the first example of a thioacid reacting with SO₃ in the same manner as an ordinary carboxylic acid. Additional calculations are needed as this work is brought to completion. 

Research by this group was featured on the MSI website in October 2015: A New Atmospheric Sulfur Compound.