Molecular Vibrational Energy with High Time and Space Resolution

技术概述本项目是利用超快激光光谱学对凝聚相分子中振动能量的实验研究。重点是了解振动能量如何在分子维度上从一个位置移动到另一个位置。为了更好地理解化学反应和理解分子机器中的散热，这些基础知识是必要的。德洛特实验室已经开发出两种技术，允许实验人员在分子的一个位置输入振动能量，并探测它在一个或多个其他位置的到达。在用于研究分子液体如一系列取代苯类的红外拉曼技术中，能量以可调谐的红外脉冲输入，并通过反斯托克斯拉曼光谱的时间序列来检测。超快闪热电导技术将用于研究吸附在金属衬底上的分子单分子膜，热的输入是通过闪光加热金属层，并用相干振动和频(SFG)光谱探测分子吸附。单层方法对研究分子结构特别有用，但SFG只提供了热流的总体测量，而反斯托克斯拉曼则揭示了哪些振动状态携带能量。德洛特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，足以探测分子单分子层。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度和热流机制。非技术摘要所有机械都会产生热量。当机器的大小是分子时，熟悉的热传输概念就不再适用了。这个项目试图使用先进的激光技术来理解分子热传输的基础科学，这种技术可以产生持续时间不到万亿分之一秒的光脉冲。有了这些先进的激光，伊利诺伊大学德洛特小组的研究人员可以将热量(振动能量)输入到分子的一个部分，并测量热量到达分子中几埃(1埃=10-10米，大约相当于分子中一个原子的直径)以外的其他部分需要多长时间。在这个项目中，德洛特团队的研究人员将开发新的技术来改进振动能量的测量，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有一个基本的理解，并提供为特定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，用于分子机械研究，随着他们成为世界级科学家的培训取得进展。对热流过程的关注是外行和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.