Bond Dissociation Energies and Electronic Structure of Small Transition Metal and Lanthanide Molecules

在化学系化学结构、动力学和机理a （CSDM-A）项目的支持下，犹他大学的Michael Morse教授正在使用激光光谱学研究含有d和f嵌段金属的小分子中的电子结构和化学键，重点是提供键解离和电离能的高精度值。这些测量将有助于为与d-和f-嵌段元素的催化和技术应用相关的大型系统开发准确和有效的计算方法。莫尔斯博士将在这项工作中研究化学键在元素周期表中的广泛趋势，并将研究与化学相关的p块元素（如硅和锗）键合的金属的离解能是否密切相关。莫尔斯教授和他的学生将使用共振双光子电离光谱来研究中性d和f块分子，并使用低温冷却离子光解实验来研究含金属阳离子。除了培训直接参与该项目的研究生外，Morse博士还为高中化学教师组织了一年两次的研讨会，在那里他介绍了他们选择的物理化学主题。其他讲者也会介绍化学教育研究和教育心理学。在这个项目中，莫尔斯小组将在氦的脉冲超音速膨胀中使用激光烧蚀金属样品，并加入少量的反应物气体，以产生感兴趣的分子束。然后，他们将使用一个激光脉冲，扫描，以电子方式激发分子，第二个激光脉冲电离分子。然后将使用飞行时间质谱法检测离子。具有高密度电子态的分子，如开放的d-和f亚壳层分子，当它们被激发到高于解离能时，会在亚纳秒的时间尺度上分裂，导致离子信号急剧下降。这提供了一个非常精确的键能测量。莫尔斯团队还能够利用这些物质中高密度的电子态来高精度地测量电离能。采用不同的仪器，研究小组正在使用类似的方法来测量d和f块低温冷却离子范围内的解离阈值。然后，中性分子及其阳离子的键解离能可以与中性分子和金属原子的电离能结合起来，使用热化学循环来确认所有四个测量值的准确性。这些研究可能对密度泛函理论方法的发展特别有用，用于精确计算含有d和f块元素的分子。该奖项反映了美国国家科学基金会的法定使命，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 Michael Morse of the University of Utah is using laser spectroscopy to study the electronic structure and chemical bonding in small molecules that contain d- and f-block metals, with emphasis on providing highly precise values of bond dissociation and ionization energies. These measurements will be useful for developing accurate and efficient computational methods for larger systems relevant to the catalytic and technological applications of the d- and f-block elements. Dr. Morse will examine the broad trends in chemical bonding as one moves across the periodic table in this work, and will investigate whether the dissociation energies of metals bonded to chemically related p-block elements, such as silicon and germanium, are strongly correlated. Professor Morse and his students will use resonant two-photon ionization spectroscopy to study neutral d- and f-block molecules, and cryo-cooled ion photodissociation experiments to study metal-containing cations. In addition to training the graduate students who are directly involved in this project, Dr. Morse also organizes a biannual workshop for high school chemistry teachers, where he presents on physical chemistry topics that they have selected. Other speakers also present on chemical education research and educational psychology.In this project, the Morse group will employ laser ablation of a metal sample in a pulsed supersonic expansion of helium with small amounts of a reactant gas to generate a molecular beam of the species of interest. They will then use a one laser pulse, which is scanned, to excite the molecule electronically and a second laser pulse to ionize the molecule. Ions will then be detected using time-of-flight mass spectrometry. Molecules with a high density of electronic states, such as the open d- and f-subshell molecules, fall apart on a subnanosecond time scale when they are excited above their dissociation energy, causing a sharp drop in ion signal. This provides a highly precise measurement of the bond energy. The Morse team is also able to use the high density of electronic states in these species to measure ionization energies to high precision. Employing a different instrument, the research team is using similar methods to measure the threshold for dissociation in a range of d- and f-block cryo-cooled ions. The bond dissociation energies of the neutral molecules and their cations can then be combined with the ionization energies of the neutral molecules and of the metal atoms using a thermochemical cycle to confirm the accuracy of all four measured values. These studies are likely to be particularly useful for the development of density functional theory methods for accurate computations of molecules containing the d- and f-block elements.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.