Molecular Vibrational Energy with High Time and Space Resolution

本项目是利用超快激光光谱学对凝聚相分子中的振动能量进行实验研究。 重点是了解振动能如何在分子尺度上从一个位置移动到另一个位置。 这些基础知识是更好地理解化学反应性和理解分子机器中的散热所必需的。 Dlott实验室已经开发了两种技术，允许实验人员在分子的一个位置输入振动能量，并探测其到达一个或多个其他位置。 在红外-拉曼技术中，将用于研究分子液体，如一系列取代苯，能量输入可调谐红外脉冲和检测的反斯托克斯拉曼光谱的时间序列。 在将用于研究吸附在金属基底上的分子单层的超快闪光热传导技术中，通过闪光加热金属层并利用相干振动和频产生（SFG）光谱探测分子吸附物来输入热量。 单层方法对于研究分子机械特别有用，但SFG仅提供热流的总体测量，而反斯托克斯拉曼则揭示了哪些振动状态携带能量。 Dlott实验室在表面增强拉曼光谱方面的最新进展将提高反斯托克斯拉曼的灵敏度，足以探测分子单层。 结合SFG，这些实验将揭示通过一系列精心制作的分子结构的热流速率和热流机制。非技术概要所有机械都产生热量。 当机器达到分子大小时，熟悉的热传输概念不再适用。 该项目旨在利用先进的激光技术来了解分子热传输的基础科学，该技术产生的光脉冲持续时间小于万亿分之一秒。 有了这些先进的激光器，伊利诺伊大学Dlott小组的研究人员可以将热量（振动能量）输入分子的一部分，并测量热量到达分子的其他部分所需的时间，这些部分位于几埃（1埃= 10-10米，大约是分子原子的直径）。 在这个项目中，Dlott小组的研究人员将开发新技术来改进振动能的测量，并将研究分子结构的系统性变化如何加速或减缓热传输。 最终，这项工作将导致在分子水平上对热的基本理解，并提供为特定的热传输应用设计分子所需的基础知识，使新技术能够帮助美国保持经济竞争力。 这项工作将由伊利诺伊大学的研究生和博士后研究人员进行，他们将学习设计，建造和操作先进的激光系统，用于分子机械的研究，因为他们在培训中取得进展，成为世界级的科学家。 对热流过程的关注，这是外行以及所有科学家都熟悉的，有助于确保我们的工作成果广泛传播到技术期刊和科普媒体。

TECHNICAL SUMMARY This project is an experimental study of vibrational energy in condensed-phase molecules using ultrafast laser spectroscopy. The focus is on understanding how vibrational energy moves over molecular dimensions from one location to another. This fundamental knowledge is needed to better understand chemical reactivity and to understand heat dissipation in molecular machines. Two techniques have already been developed in the Dlott laboratory that allow experimenters to input vibrational energy at one location of a molecule and probe its arrival at one or more other locations. In the IR-Raman technique that will be used to study molecular liquids such as a series of substituted benzenes, the energy is input with a tunable IR pulse and detected by a time series of anti-Stokes Raman spectra. In the ultrafast flash-thermal conductance technique that will be used to study molecular monolayers adsorbed on metal substrates, heat is input by flash-heating the metal layer and probing the molecular adsorbate with coherent vibrational sum-frequency generation (SFG) spectroscopy. The monolayer method is especially useful for studying molecular machinery, but SFG provides only an overall measure of heat flow, as opposed to anti-Stokes Raman that reveals which vibrational states carry the energy. Recent advances in surface-enhanced Raman spectroscopy from the Dlott laboratory will improve the sensitivity of anti-Stokes Raman enough to probe molecular monolayers. Combined with SFG, these experiments will reveal both the rate of heat flow and the mechanism of heat flow through a series of crafted molecular structures.NON-TECHNICAL SUMMARY All machinery generates heat. When the machine is the size of a molecule, the familiar concepts of heat transport no longer apply. This project seeks to understand the fundamental science of heat transport through molecules using advanced laser technology that produces light pulses less than one trillionth of a second in duration. With these advanced lasers, researchers in the Dlott group at the University of Illinois can input heat (vibrational energy) into one part of a molecule and measure how long it takes the heat to reach other parts of the molecule located a few angstroms (1 angstrom = 10-10 meters is about the diameter of one of the molecule's atoms) away. In this project, Dlott group researchers will develop new techniques to improve the measurement of vibrational energy, and will study how systematic changes of the molecular structure can speed up or slow down the heat transport. Ultimately this work will lead to a fundamental understanding of heat at the molecular level and provide the underlying knowledge needed to engineer molecules for specific heat transport applications, enabling new technologies to help the US remain economically competitive. The work will be performed by graduate students and postdoctoral researchers at the University of Illinois, who will learn to design, construct and operate advanced laser systems for studies of molecular machinery as they progress in their training to become world-class scientists. The focus on heat flow processes, which are familiar to laypersons as well as all scientists, helps insure the wide dissemination of the results of our work to technical journals and popular science media.