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

在化学系化学结构、动力学和机理计划(CSDM-A)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-块金属的小分子中的电子结构和化学键，重点是提供高精度的键离解能和电离能值。这些测量将有助于为与d-块和f-块元素的催化和技术应用有关的较大系统开发准确和有效的计算方法。在这项工作中，莫尔斯博士将考察化学键在元素周期表中移动的广泛趋势，并将研究与硅和锗等化学相关的p-块元素键合的金属的离解能是否具有很强的相关性。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的d-和f-块分子，并使用低温离子光解实验来研究含有金属的阳离子。除了培训直接参与这个项目的研究生，莫尔斯博士还为高中化学教师组织了一年两次的研讨会，在会上他就他们选择的物理化学主题发表演讲。其他演讲者还介绍了化学教育研究和教育心理学。在这个项目中，Morse小组将使用激光烧蚀金属样品，在脉冲超音速膨胀氦中加入少量反应气体，以产生感兴趣物种的分子束。然后，他们将使用扫描的一个激光脉冲以电子方式激发分子，并使用第二个激光脉冲使分子电离。然后将使用飞行时间质谱学来检测离子。具有高电子态密度的分子，如开放的d-和f-亚壳层分子，当它们被激发到高于其解离能时，在亚纳秒的时间尺度上解体，导致离子信号的急剧下降。这提供了对键能的高度精确的测量。莫尔斯团队还能够利用这些物种中高密度的电子态来高精度地测量电离能。使用一种不同的仪器，研究小组正在使用类似的方法来测量一系列d-和f-块低温冷却离子的离解阈值。然后，可以使用热化学循环将中性分子及其阳离子的键离解能与中性分子和金属原子的电离能结合起来，以确认所有四个测量值的准确性。这些研究可能对开发密度泛函理论方法用于精确计算包含d和f块元素的分子特别有用。这一奖项反映了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 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.