Characterizing Potential Energy Surfaces for Hydrocarbon Activation by Transition Metal, Metal Cluster and Metal Oxide Cations via Spectroscopy and Photofragment Imaging

该奖项由化学学部化学结构、动力学和机制项目a资助，来自马萨诸塞大学阿姆赫斯特分校的Ricardo B. Metz教授将利用双飞行时间质谱仪中的振动和电子能谱，表征分子反应物、产物，特别是金属、金属簇和金属氧化物阳离子与碳氢化合物反应的反应中间体的结构和键合。感兴趣的系统包括离子将甲烷转化为更大的碳氢化合物，甲烷转化为甲醇，乙烯转化为苯。这些系统将研究几种金属，并作为簇大小的函数，以测量中间产物的结构和键合的周期性趋势，并将它们与测量的依赖于尺寸的反应性联系起来。光碎片成像也将用于研究离子在电子激发后的光解动力学，测量动能释放和碎片各向异性。这是对激发态动力学和激发态之间耦合的详细探索，也将提供准确的键强度。这些“半碰撞”实验补充了全碰撞反应的研究，直接探测了反应的势能面，并从具有明确能量、几何形状和角动量的中间体开始反应。美国拥有大量的天然气产量和丰富的储量，天然气被广泛用于供暖和发电。然而，它通常不被用作运输燃料。这是因为甲烷（天然气中含有70-90%的甲烷）是一种在室温下不能转化为液体的气体。要使用甲烷作为运输燃料，需要将其转化为液体。催化剂用于将一种化学物质转化为另一种更理想的化学物质；需要新的催化剂直接、选择性和高效地将甲烷转化为有用的液体，如甲醇。了解工业催化中涉及的复杂反应，并改进催化剂，需要结合基础研究、计算和活性催化剂的研究。这项研究的结果将有助于扩大我们对金属原子和金属簇与碳氢化合物反应的详细方式的基本理解，通过使用光谱来揭示这些反应从反应物到产物的中间产物的结构和键合。

Through this award, funded by the Chemical Structure, Dynamics, and Mechanisms Program-A of the Division of Chemistry, Prof. Ricardo B. Metz from the University of Massachusetts Amherst, will characterize the structure and bonding of the molecular reactants, products and, especially, reaction intermediates of the reactions of metal, metal cluster and metal oxide cations with hydrocarbons using vibrational and electronic spectroscopy in a dual time-of-flight mass spectrometer. Systems of interest include ions that convert methane to larger hydrocarbons, methane to methanol, and ethylene to benzene. These systems will be studied for several metals and as a function of cluster size, to measure periodic trends in the structure and bonding of intermediates and to correlate them to the measured size-dependent reactivities. Photofragment imaging will also be used to study ions' photodissociation dynamics following electronic excitation, measuring kinetic energy release and fragment anisotropy. This is a detailed probe of excited state dynamics and the couplings between excited electronic states and will also provide accurate bond strengths. These "half-collision" experiments complement full-collision reaction studies by directly probing the potential energy surface for the reaction and by initiating the reaction from an intermediate with well-defined energy, geometry and angular momentum.The U.S. has large production and extensive reserves of natural gas, and it is widely used for heating and to generate electricity. However, it is not typically employed as a transportation fuel. This is because methane (natural gas is 70-90% methane) is a gas that cannot be turned into a liquid at room temperature. To use methane as a transportation fuel, it needs to be converted into a liquid. Catalysts are used to convert one chemical into another, more desirable chemical; new catalysts are needed to directly, selectively and efficiently convert methane into useful liquids such as methanol. Understanding the complex reactions involved in industrial catalysis, and improving catalysts, requires combining fundamental studies, calculations, and studies of active catalysts. Results from this study will contribute to this effort by expanding our fundamental understanding of the detailed ways in which metal atoms and metal clusters react with hydrocarbons by using spectroscopy to reveal the structure and bonding in the intermediates these reactions pass through on the way from reactants to products.