Calcium: Chemically and Electronically a Transition Metal?

在化学系化学结构，动力学和机制-A（CSDM-A）计划的支持下，匹兹堡大学的Hrvoje Petek教授正在使用表面电子光谱和扫描隧道显微镜研究钙的化学反应性和性质。金属钙在环境条件下非常活泼，因此对其化学和物理性质的了解仍然是难以捉摸的。因此，Petek教授和他的团队将使用超真空方法制备钙膜，并使用原子尺度成像和光谱方法在高度受控的条件下研究反应性。从事这项研究的学生将接触到最先进的光谱方法，并学习将这些方法应用于物理和无机化学界面的基本问题，包括在这种情况下，思考钙在单分子水平上的碳捕获中所起的作用。钙，具有完全占据的4s壳层，容易将电子转移到相互作用的分子;然而，这个过程是否涉及s轨道或d轨道还不清楚。为了阐明这一机制，钙烯，其中钙原子排列在蜂窝结构中的结构，似乎涉及强d-轨道字符，将在良好的控制条件下，使用双光子光电子能谱和扫描隧道显微镜进行研究。这两种方法预计将揭示系综平均和原子尺度的占有和未占有的电子结构的定义明确的材料，在真空下，以帮助分类的钙状态，无论是碱金属或过渡金属。通过将钙膜暴露于小分子如二氧化碳、水和氧气;它们的反应性和电子行为有望揭示所形成的键的电子特性。如果成功的话，这些研究有望导致该方法在其他元素/催化系统中的更广泛应用。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.