Studies of Nanometer Scale Metal Cluster Dissociation in the Gas Phase

明尼苏达大学双子城分校的教授克里斯托弗·霍根、史蒂文·格希克和唐纳德·特鲁拉获得了高分子、超分子和纳米化学项目的奖项，以更好地了解金属团簇的形成和生长。该团队正在通过实验和计算相结合的方法研究气相中纳米级团簇的性质(从6个原子到1000个原子)。具体地说，用串联微分迁移率分析方法对金属团簇的离解过程进行了实验监测。这些实验首次测量了大气压下气相中性、阳离子和阴离子金属团簇的单原子蒸发。同时，金属团簇的离解速率可以从分子动力学轨迹模拟中推断出来，从而允许实验测量和计算预测的直接比较。在测量和计算中特别感兴趣的是识别反常幻数和反幻数星团，它们分别是反常稳定的或不稳定的。这些幻数团簇的存在极大地改变了气相金属团簇的成核速度。研究小组从测量和计算的金属团簇的解离速度推断出团簇的形成和增长速度，从而能够在新设计的湍流混合金属团簇生长反应器中将团簇增长速度预测与实验测量进行比较。这些实验和模拟阐明了金属团簇的行为，从而为未来设计具有纳米级特征的多组分金属材料的合成系统提供了基础。这一领域的研究在环境和材料科学中有技术应用，例如垃圾焚烧和燃煤废气。这个项目本质上是跨学科的，连接了物理化学和机械工程的学科。它的独特之处在于，它结合了新开发的实验技术和尖端分子模拟，其中重叠到目前为止是稀疏的。此外，这些研究是将材料在分子尺度上的性质与块状材料的性质联系起来的重要努力的一部分。这些研究的其他更广泛的影响包括对参与该项目的研究生和博士后研究人员进行跨学科教育，包括开发新的跨学科课程，重点从化学家和工程师的角度研究纳米团簇的性质。

Professors Christopher Hogan, Steven Girshick, and Donald Truhlar of the University of Minnesota-Twin Cities are receiving an award from the Macromolecular, Supramolecular and Nanochemistry Program to better understand metal cluster formation and growth. The team is examining the properties of nanometer scale clusters (from as small as 6 atoms up to 1000 atoms) in the gas-phase by a combined experimental and computational approach. Specifically, the dissociation of metal clusters, Mn -- Mn-1 + M (where M is a metal and n is the number of atoms in a metal cluster) is monitored experimentally using tandem differential mobility analysis. These experiments are the first ever measurements of single atom evaporation from gas phase neutral, cationic, and anionic metal clusters at atmospheric pressure. Simultaneously, the dissociation rates of metal clusters are inferred from molecular dynamics trajectory simulations allowing for direct comparison of experimental measurements and computational predictions. Of particular interest in measurements and computations is the identification of anomalous magic number and anti-magic number clusters, which are either anomalously stable or unstable, respectively. The existence of these magic number clusters vastly alters the rate of nucleation for gas phase metal clusters. The team of researchers infers the rate of cluster formation and growth from the measured and computed rates of dissociation for metal clusters, enabling comparison of cluster growth rate predictions to experimental measurements in a newly designed turbulent mixing metal cluster growth reactor. These experiments and simulations elucidate the behavior of metallic clusters, thus providing the basis for the design of future synthesis systems for multi component metallic materials with nanoscale features. This area of research has technological applications in environmental and materials sciences, e. g., waste incineration and coal burning exhausts. This project is interdisciplinary in nature, bridging the disciplines of physical chemistry and mechanical engineering. It is unique in that it incorporates both newly developed experimental techniques and cutting-edge molecular simulations, where overlap has thus far been sparse. Moreover, these studies are part of a vital effort to link the properties of materials at the molecular scale to properties of bulk materials. Additional broader impacts of these studies include the interdisciplinary education of graduate students and postdoctoral researchers involved in the project, including the development of new interdisciplinary courses focusing on the properties of nanometer scale clusters from both the chemist's and engineer's perspective.