PChem Seminar – Dr. Richard Cox
About the event
Speaker: Dr. Richard M. Cox, Nuclear Chemistry and Engineering, Pacific Northwest National Laboratory
Host: Dr. Ivan Popov
Title: Oops! Lessons Learned (so far) of f-Block Behavior from a Career Defining Mistake.
The f-block elements present a final frontier of chemistry. Predicting which orbitals participate in bond activation and product formation is important in developing a better understanding of the defining f block chemical properties and is also an important test of how well we understand chemical theory. Previous work has suggested that the 5d and 6d orbitals are very important to bond activation and chemical bonding in oxidation reactions for both the lanthanides (Ln) and actinides (An). However, the actinides specifically are very difficult to study experimentally because of their limited availability and the extreme radioactivity of most members of the series. Gas phase experiments offer a unique and direct route to study the fundamental interactions between a given element of interest and ligand because bulk phase perturbations (e.g. solvent effects) are eliminated. The inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) experiment currently being developed at Pacific Northwest National Laboratory has enabled the examination of chemical reactions over a wide energy range and has been used to extend the thermodynamic and kinetic information available for the oxidation studies of f-block, and more interestingly the actinide elements. Trends across the An series indicate that the 6d electrons are still incredibly important in final product formation; nevertheless, the f orbitals, under some circumstances, may play a critical role in bond activation even if they are only minor participants in the chemical bonding of the final product. New thermochemistry derived from these ICP-MS/MS studies suggest that there is a “switch” in reactivity and bonding between Np+ and Pu+. This may suggest a shift from An-L+ bonding defined by orbital overlap for the early An to bonding driven by orbital energy degeneracy for the later An.
Dr. Richard “Rich” Cox studied f block reactions with small molecules by guided ion beam tandem mass spectrometry under Prof. Peter Armentrout at the University of Utah. He joined Pacific Northwest National Laboratory (PNNL) as a postdoctoral research associate in 2015 converting to a staff scientist in 2018. He is currently the team lead of the Nuclear Chemistry Team within the Nuclear Chemistry and Engineering Group. This team caretakes PNNL’s mass spectrometry capability within the Radiological Processing Laboratory. In addition to continuing his studies in actinide gas phase chemistry, he leads or contributes to projects that range from national security to environmental management.