Reactive Systems at the Onset of Microsolvation

摘要：Leopold， Kenneth r .溶剂化对分子结构和反应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物质的研究提供了一种有价值的手段。这样的工作提供了发展一种越来越精确的分子水平的溶剂化描述的可能性。在这个项目中，旋转光谱学将用于研究微溶剂化对反应性酸碱配合物的影响。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，原子核的超精细结构也会揭示电荷分布的各个方面。两类系统的目标：(i)部分结合的刘易斯酸碱配合物，其结构和键在结晶时发生巨大变化；（ii）氢键系统，在溶液或结晶相中进行质子转移。选择这些系统是因为在这两种情况下，聚集促进化学变化，因此，微溶剂化的影响预计会很明显。这项工作要解决的核心问题是，“在聚集驱动化学变化的系统中，第一个近邻的影响有多大？”还考虑了几种具有较高溶剂化程度的体系。这项工作将系统地利用这些反应性酸碱配合物对其近邻相互作用的超敏感性，以研究小簇水平上的“溶剂化”效应。许多对人类活动很重要的化学反应都涉及到溶液中的物质。例如，生物的化学反应，被污染的地下水中的化学反应，甚至许多重要的工业过程都是在分子溶解在溶剂中时才发生的。当这种反应发生时，溶剂本身并不是化学反应的直接参与者，尽管越来越清楚的是，它的存在在调解发生的反应中起着重要的作用。因此，在这个项目中，我们感兴趣的是研究溶剂在中介化学过程中的作用。我们的方法是通过检查靠近一对活性分子的单个溶剂分子的影响来获得对问题的基本理解。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是如何影响它们的。了解单个溶剂分子的影响是重要的一步，因为它是理解实际溶液中存在的许多溶剂分子的影响的基本组成部分。此外，从这项工作中获得的基本知识可能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，它们的存在对气候、臭氧水平和人类健康有广泛的影响。通过这种方式，我们设想了本项目中所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，作为他们博士学位培训的一部分，并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.