Calcium: Chemically and Electronically a Transition Metal?

在化学系化学结构、动力学和机理(CSDM-A)项目的支持下，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活性和性质。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难以捉摸。因此，Petek教授和他的团队将使用超高真空方法来制备钙膜，并使用原子尺度成像和光谱方法来研究高度受控条件下的反应性。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化学和无机化学界面的基本问题，在这种情况下，包括在单分子水平上思考钙在碳捕获中所起的作用。钙具有完全占据的4S壳层，很容易将电子转移到相互作用的分子；然而，尚不清楚这一过程是否涉及S轨道或d轨道。为了阐明这一机制，将利用双光子光电子能谱和扫描隧道显微镜在可控的条件下研究钙烯，这是一种钙原子以蜂窝结构排列的结构，似乎涉及到强d轨道特征。这两种方法有望揭示超高真空下定义良好的材料的系综平均和原子尺度占据和未占据的电子结构，以帮助将钙状态分类为碱金属或过渡金属。通过将钙膜暴露在二氧化碳、水和氧气等小分子中，它们的反应性和电子行为有望揭示形成的键的电子特征。如果成功，这些研究有望将该方法更广泛地应用于其他元素/催化系统。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.