Calcium: Chemically and Electronically a Transition Metal?

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With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Professor Hrvoje Petek of the University of Pittsburgh is investigating the chemical reactivity and properties of calcium using surface electronic spectroscopy and scanning tunneling microcopy. Calcium metal is very reactive in ambient conditions, so understanding its chemical and physical properties has remained elusive. As a result, Professor Petek and his team will use ultrahigh vacuum methods to prepare calcium films and atomic scale imaging and spectroscopic methods to investigate reactivity under highly controlled conditions. Students engaged in this research will gain exposure to state-of-the-art spectroscopic methods and learn to apply these to fundamental questions at the interface of physical and inorganic chemistry, including, in this case, thinking about the role calcium plays in carbon capture at a single molecule level.Calcium, which has a fully occupied 4s shell, readily transfers an electron to interacting molecules; however, it is unclear whether this process involves the s- or d- orbitals. To elucidate this mechanism, calcene, a structure in which calcium atoms are arranged in a honeycomb structure and appears to involve strong d-orbital character, will be investigated under well-controlled conditions using two-photon photoemission spectroscopy and scanning tunneling microscopy. These two methods are expected to reveal the ensemble averaged and atomic scale occupied and unoccupied electronic structures of well-defined materials, under ultrahigh vacuum to help classify the calcium states as either alkali or transition metal. By exposing the calcium films to small molecules such as carbon dioxide, water, and oxygen; their reactivity and electronic behavior is expected to reveal the electronic character of the bonds that form. If successful, these studies are expected to lead to broader application of the approach to other elements/catalytic systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.