State-Resolved Spectroscopy and Dynamics of Chemical Transients

在这个由化学部门化学结构动力学和机制A （CSDM-A）项目资助的项目中，科罗拉多大学的David Nesbitt教授使用复杂的激光光谱和分子束技术来探测气液界面上的反应性化学中间物质。化学中奇怪的悖论是，最相关的化学中间体必然以极低的浓度存在，因此需要越来越高灵敏度的检测方法来观察。没有什么地方比气液界面更需要这种灵敏度了，在这个界面上，一层超薄层（10-7厘米）作为气相分子和大量液体内部深处之间的“门户”。拟议的研究旨在系统地探索这些界面，利用高分辨率激光光谱和分子束工具从液体中“反弹”分子，并探测产品从表面散射的化学成分、振动、旋转、速度和方向。内斯比特教授担任科罗拉多大学奇才科学推广项目主任已经31 -33年了，该项目每学年（从9月到6月）为初中和初中的孩子们组织10场充满演示性的科学讲座，涉及的科学领域从黑洞到烹饪物理学到气候变化背后的原因。特别是，拟议的研究正在利用简单分子（如DCl， HCl， CO, CO2， OCS， NO）以高达2000 m/s（比声速快2-10倍）的速度与简单液体（如水，盐水，甘油，碳氢油，熔盐，甚至1100℃的熔融金！）碰撞的超音速膨胀。内斯比特的学生们正在利用高分辨率激光光谱学来探索冷分子抛射物是如何“升温”到甚至大大超过散装液体的温度的。这些结果被证明是敏感地依赖于并因此定量地探测这个薄界面层的性质（例如，它是“粗糙”还是“光滑”，“软”还是“硬”，“酸性”还是“碱性”，或“憎水”（疏水）还是“亲水”（亲水），等等），从而提供了对界面分子碰撞动力学和化学的详细见解。例如，这与O2和CO2等分子如何穿过肺部，溶解到血液中，并最终进入/离开任何生物体的细胞有关。气液界面可以说是最不为人所知的物质相，但它代表了气体分子可以溶解到液体中（或被排出）的唯一“门户”。因此，气液界面代表了一个鲜为人知的新科学前沿，但它对肺部医学、海洋表层化学、大气气溶胶化学、臭氧空洞形成和全球气候变化等不同领域都有影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

In this project funded by the Chemical Structure Dynamics and Mechanisms A (CSDM-A) program of the Chemistry Division, Professor David Nesbitt of the University of Colorado uses sophisticated laser spectroscopy and molecular beam techniques to probe reactive chemical intermediate species at the gas-liquid interface. The curious paradox of chemistry is that the chemical intermediates of greatest relevance are necessarily present in vanishingly low concentrations and therefore require higher and higher sensitivity detection methods to observe. Nowhere are these sensitivity needs more pronounced than at the gas-liquid interface, whereby an ultrathin layer (10-7 cm) serves as the “doorway” between molecules in the gas phase and deep inside the bulk liquid. The proposed research is directed towards systematic exploration of such interfaces, exploiting high resolution laser spectroscopy and molecular beam tools to “bounce” molecules from liquids and probing the chemical composition, vibrational, rotational, speeds, and directions in which the product scatters from the surface. Prof. Nesbitt is continuing his 31st-33rd years as director of the CU Wizards Science Outreach program, which entails organizing 10 demo-filled science presentations each academic year (from September to June) for children in lower and middle school, in areas of science ranging from Black Holes to the Physics of Cooking to the What's Behind Climate Change? In particular, the proposed studies are exploiting supersonic expansions of simple molecules (e.g., DCl, HCl, CO, CO2, OCS, NO) moving at up to 2000 m/s (2-10x faster than the speed of sound) colliding with simple liquids (e.g., water, salty water, glycerin, hydrocarbon oils, molten salts, and even molten gold at 1100 C!). Nesbitt’s students are utilizing high resolution laser spectroscopy to explore how cold molecular projectiles “warm up to” and even significantly exceed the temperature of the bulk liquid. These results turn out to depend sensitively on and therefore quantitatively probe the nature of this thin interfacial layer (e.g., is it “rough” vs “smooth”, “soft” vs “hard”, “acidic” or “basic”, or “water-hating” (hydrophobic) vs. “water-loving” (hydrophilic), etc.), thereby providing detailed insights into the collision dynamics and chemistry of molecules at interfaces. This is relevant to how, for example, molecules such as O2 and CO2 cross through the lungs, dissolve into the blood stream, and eventually enter/leave the cells in any living organism. The gas-liquid interface is arguably the least well understood phase of matter and yet represents the sole “portal” through which gas molecules can dissolve into (or be expelled out of) a liquid. The gas-liquid interface thus represents a new scientific frontier about which remarkably little is known, but which nevertheless has impacts in areas as disparate as pulmonary medicine, ocean surface layer chemistry, atmospheric aerosol chemistry, ozone hole formation, and global climate change.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.