Reactive Systems at the Onset of Microsolvation

摘要：CHE-0132584PI：Leopold，Kenneth R.溶剂化对分子结构和反应活性的影响是化学中的一个重要问题。微溶剂化物质的研究为气相测量和凝聚态研究提供了一种有价值的手段。这项工作提供了发展一种越来越准确的溶剂化分子水平描述的可能性。在这个项目中，旋转光谱学将被用来检测微溶剂化对反应性酸碱络合物的影响。分子结构和偶极矩将分别由旋转常数和斯塔克效应数据确定。在某些情况下，电荷分布的各个方面也会被核超精细结构所揭示。两类体系是针对的：(I)部分结合的Lewis酸碱络合物，其结构和成键在结晶时发生显著变化；(Ii)氢键体系，其在溶液中或在晶相中经历质子转移。之所以选择这些体系，是因为在这两种情况下，聚集都会促进化学变化，因此，微溶剂化的影响预计会很明显。这项工作要解决的中心问题是，“在聚集驱动化学变化的系统中，第一个近邻的影响有多大？”还考虑了几个溶剂化程度较高的体系。这项工作将系统地利用这些反应性酸碱络合物对其近邻相互作用的超敏性，目的是在小团簇水平上研究“溶剂化”效应。对人类活动重要的许多化学物质涉及溶液中的物质。例如，生物的化学，受污染的地下水中的反应，甚至许多重要的工业过程，只有当分子溶解在溶剂中时才会发生。当这种反应发生时，溶剂本身并不是化学的直接参与者，尽管越来越明显的是，它的存在可以在调节发生的反应中发挥重要作用。因此，在这个项目中，我们感兴趣的是研究溶剂在化学过程中的中介作用。我们的方法是通过研究靠近一对反应分子的单个溶剂分子的影响来获得对这个问题的基本理解。为了做到这一点，我们分离了两个反应分子和一个溶剂分子，并使用微波来研究溶剂如何影响它们。了解单一溶剂分子的影响是重要的一步，因为它是了解实际溶液中存在的许多溶剂分子的影响的基础。此外，从这项工作中获得的基本知识可能会对模拟具有社会重要性的难题产生直接影响，例如，地球大气中粒子的形成，它的存在对气候、臭氧水平和人类健康有广泛的影响。通过这种方式，我们展望了这个项目中涉及的基础科学的潜在实际应用。明尼苏达大学的研究生将参与这项研究，作为他们攻读博士学位的培训的一部分，他们将学习许多适用于各种问题的技术技能。

AbstractProposal: CHE-0132584PI: Leopold, Kenneth R.The effect of solvation on molecular structure and reactivity is an important problem in chemistry. The investigation of microsolvated species offers a valuable means of bridging gas phase measurements with studies of condensed matter. Such work offers the possibility of developing an increasingly accurate molecular-level description of solvation. In this project, rotational spectroscopy will be used to examine the effects of microsolvation on reactive acid-base complexes. Molecular structures and dipole moments will be determined from rotational constants and Stark effect data, respectively. Aspects of charge distribution will, in certain cases, also be revealed by nuclear hyperfine structure. Two classes of systems are targeted: (i) partially bound Lewis acid-base complexes, whose structure and bonding change dramatically upon crystallization and (ii) hydrogen bonded systems which undergo proton transfer in solution or in the crystalline phase. These systems are chosen because in both cases, aggregation promotes chemical change and the effects of microsolvation are, therefore, expected to be pronounced. The central question to be addressed in this work is , "In systems for which aggregation drives chemical change, how big is the effect of the first near neighbor?". Several systems with higher degrees of solvation are also considered. This work will systematically exploit the hypersensitivity of these reactive acid-base complexes to their near-neighbor interactions for the purpose of investigating "solvation" effects at the small cluster level.Much of the chemistry important to human activity involves substances in solution. For example, the chemistry of living things, reactions in contaminated ground waters, and even a host of important industrial processes occur only when molecules are dissolved in a solvent. When such reactions occur, the solvent itself is not a direct participant in the chemistry, though it has become increasingly clear that its presence can play a significant role in mediating the reactions that take place. Thus, in this project, we are interested in studying the role of solvent in mediating chemical processes. Our approach is to gain a basic understanding of the problem by examining the effect of a single solvent molecule close to a pair of reactive molecules. To accomplish this, we isolate two reacting molecules, plus one solvent molecule, and use microwaves to investigate how the solvent affects them. Understanding the influence of a single solvent molecule is an important step, as it is the fundamental building block for understanding the influence of the many solvent molecules present in a real solution. Moreover, the basic knowledge gained from this work may have direct consequences for modeling difficult problems of societal importance, e.g., the formation of particles in the earth's atmosphere, whose presence has wide ranging effects on climate, ozone levels, and human health. In this way, we envision potential practical applications for the fundamental science addressed in this project. Graduate students at the University of Minnesota will participate in this research as part of their training toward the doctoral degree and will learn numerous technical skills applicable to a wide variety of problems.