Reactions of Interfacial Electrons Initiated by Collisions of Sodium Atoms with Water Microjets in Vacuum

自然世界和工业社会的许多方面都依赖于水中发生的反应。水中最具反应性的物质可能是被水分子包围的电子本身。 它被称为“溶剂化电子”，存在时间稍纵即逝，在水中仅持续1/1000秒。 在这么短的时间内，深埋在水中的溶剂化电子可以与各种类型的分子发生反应，迄今为止记录的反应次数已达到 1600 次。人们对水表面的溶剂化电子知之甚少，因为水表面的溶剂化电子可能更具反应性。在化学系化学结构、动力学和机理 (CSDM-A) 项目的支持下，威斯康星大学麦迪逊分校的 Gilbert Nathanson 教授正在探索溶剂化电子的反应，以了解其体积和表面反应性的差异。 内森森教授与他的学生合作，将一束钠原子从狭窄的水射流中散射出来，产生溶剂化电子，然后与水面的有机分子发生反应。 该小组的发现可以提供不同寻常的途径来销毁漂浮在水面的有毒废物，从而产生重要的社会效益。 该项目还培训研究生和本科生成为富有创造力、批判性和独立的科学家。 当地科学节、小学和老年人中心的外展活动通过适合所有年龄段的动手表面化学实验激发兴奋和好奇心。作为一种强大的亲核试剂和还原剂，溶剂化电子经常以接近扩散极限的速率破坏化学键并产生反应性自由基。这项研究旨在利用气液散射实验以及水微射流和质谱法来研究溶剂化电子如何在水-真空界面上发生反应。 正在探索的独特界面途径包括反应中间体逃逸到气相中以及溶剂化电子与定向表面活性剂分子上的官能团的反应。钠原子与水微射流碰撞产生界面溶剂化电子。 这些原子在最初的几个单层内电离，并与表面活性分子发生反应。 作为一个例子，由一个苄基和三个烷基链组成的有机铵阳离子在水表面形成单层。 溶剂化电子可以破坏苄基-氮键，将苄基自由基和中性胺释放到界面区域。 通过自由基和胺的蒸发作为表面活性剂堆积、烷基链长度和抗衡离子特性的函数来监测该反应，以了解溶剂化电子在突然变化的表面活性剂-水环境中如何反应。 这些研究揭示了当溶剂化电子在表面活性剂层内或表面活性剂层下方电离钠原子时，表面和本体反应位点的竞争。 并行研究正在探索带负电的苯甲酸根阴离子单层和烷基化氨基酸半胱氨酸单层，这是一种两性离子，在溶剂化电子攻击后释放硫化氢。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Many aspects of our natural world and industrial society rely on reactions that occur in water. Probably the most reactive species in water is the electron itself, surrounded by water molecules. It is called the "solvated electron" and it has a fleeting existence, lasting only 1/1000 of a second in water. During this short time, a solvated electron buried deep inside water can react with molecules of all types, reaching 1600 recorded reactions so far. Much less is known about solvated electrons at the surface of water, where it might be even more reactive. With support from the Chemical Structure, Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Gilbert Nathanson of the University of Wisconsin-Madison is exploring reactions of solvated electrons to learn how its bulk and surface reactivity differ. Working with his students, Professor Nathanson scatters a beam of sodium atoms off a narrow jet of water to create the solvated electron, which then reacts with organic molecules at the water surface. The group's discoveries could provide unusual routes to destroy toxic waste that floats water surfaces, resulting in important societal benefits. The project is also training graduate and undergraduate students to become creative, critical, and independent scientists. Outreach efforts at local science festivals, elementary schools, and senior centers stimulate excitement and curiosity through hands-on surface chemistry experiments for all ages.As a powerful nucleophile and reductant, the solvated electron often breaks bonds and creates reactive free radicals at near diffusion-limited rates. This research is directed at investigating how solvated electrons react at the water-vacuum interface using gas-liquid scattering experiments coupled with water microjets and mass spectroscopy. Among the uniquely interfacial routes that are being explored are the escape of reaction intermediates into the gas phase and reactions of solvated electrons with functional groups on oriented surfactant molecules. Interfacial solvated electrons are generated by collisions of sodium atoms with a water microjet. These atoms ionize within the first few monolayers, where they react with surface-active molecules. As one example, organic ammonium cations composed of a benzyl group and three alkyl chains form monolayers at the surface of water. Solvated electrons can break the benzyl-nitrogen bond, releasing the benzyl radical and neutral amine into the interfacial region. This reaction is monitored by evaporation of the radical and amine as a function of surfactant packing, alkyl chain length, and counterion identity to learn how solvated electrons react in the abruptly changing surfactant-water environment. These studies reveal the competition for surface and bulk reaction sites as solvated electrons are released sodium atom ionization within or below the surfactant layer. Parallel studies are exploring a negatively charged monolayer of benzoate anions and a monolayer of the alkylated amino acid cysteine, a zwitterion that releases hydrogen sulfide following solvated electron attack.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.