Photoinitiated Dynamics of Transient Species: Hydrogen-Bonded Clusters

在这个项目中，由化学结构、动力学和机制-A （CSDM-A）和化学学部的大分子、超分子和纳米化学（MSN）项目支持，南加州大学的Hanna Reisler教授使用激光引发化学反应，然后观察分子如何解离（分解），消散他们从激光吸收的能量，或者在光照射下表现为酸。Reisler小组对含有少量盐酸（HCl）分子和有机分子（如苯或苯酚）的水中的分子和纳米颗粒的氢键配合物特别感兴趣。氢键是由部分带负电荷的原子（如一个分子上的氧原子）和邻近分子上的部分带正电荷的氢原子相互吸引而形成的。氢键网络影响化学和生物功能，并涉及太阳系中冰体的身份。由于很难确定实验条件，氢键还没有被很好地理解。Reisler教授通过选择含有特定数量溶质分子的水聚集体来克服这些挑战，然后使用对感兴趣的分子和反应具有高检测灵敏度的激光技术。该项目更广泛的影响包括潜在的社会效益，因为它能更好地理解氢键对大气和其他富含水的环境（如人体）中分子反应性的影响。学生和博士后研究人员建造先进的仪器，为他们的高科技事业做准备。Reisler教授是在科学领域指导女性的领导者，她继续鼓励来自代表性不足群体的学生从事科学、技术、工程和数学方面的职业。目前的研究主要集中在三个方面：(1)水二聚体与芳香分子预解的能量流动途径；(2)测量具有特定HCl和水亚基的环三聚体和四聚体的氢键离解能；(3)纳米尺度水样与质子的相互作用。通过记录解离簇的一个片段的特定旋转振动水平的图像，确定了共片段中的旋转振动能量分布，展示了几何形状和氢键类型如何影响能量分配。这为理论和提出的机制提供了严格的检验。为了研究凝聚相聚集体中酸性的产生，纳米金纳米粒子阵列被固体水覆盖，并通过可见光照射激发金纳米粒子的等离子体共振来实现快速加热。一个直径0.5毫米的激光脉冲能激发超过一百万个纳米粒子。用同位素交换法研究了单脉冲激光对掺杂HCl固体水的影响。

In this project, supported by the Chemical Structure, Dynamics and Mechanisms - A (CSDM-A) and Macromolecular, Supramolecular and Nanochemistry (MSN) Programs of the Division of Chemistry, Professor Hanna Reisler of the University of Southern California uses lasers to initiate chemical reactions and then observe how the molecules dissociate (fall apart), dissipate the energy they absorbed from the laser light, or behave as acids under light exposure. The Reisler group is particularly interested in hydrogen-bonded complexes of molecules and nanoparticles in water containing a few molecules of hydrochloric acid (HCl) and organic molecules such as benzene or phenol. Hydrogen bonds are formed from the attraction of partially negatively-charged atoms such as oxygen on one molecule and the partially positive charge of a hydrogen atom on a neighboring molecule. Hydrogen-bonded networks influence chemical and biological function and are implicated in the identity of icy bodies in the solar system. Hydrogen bonding is not yet well understood because of difficulties in defining the experimental conditions. Professor Reisler overcomes these challenges by selecting water aggregates that contain a specific number of solute molecules, then uses laser techniques that have high detection sensitivity for the molecules and reactions of interest. The broader impacts of the project include potential societal benefits arising from better understanding the effects of hydrogen bonding on the reactivity of molecules in the atmosphere and other water-rich environments, like the human body. Students and postdoctoral researchers build advanced instrumentation, preparing them high technology careers. Professor Reisler, a leader in mentoring of women in science fields, continues her activities in encouraging students from underrepresented groups to pursue careers in science, technology, engineering and mathematics.The current research focuses on three topics: (1) energy flow pathways in the predissociation of dimers of water with aromatic molecules;(2) measurements of hydrogen-bond dissociation energies in cyclic trimers and tetramers with specific HCl and water subunits; and (3) interactions of nanoscale water samples with protons. By recording images of specific rovibrational levels of one fragment of the dissociated cluster, the rovibrational energy distributions in the cofragments are determined, demonstrating how geometry and hydrogen-bonding type influence energy disposal. This provides stringent tests of theories and proposed mechanisms. In order to study the emergence of acidity in condensed phase aggregates, nanofabricated arrays of gold nanoparticles are covered with solid water and rapid heating is achieved by visible irradiation that excites the plasmon resonance of the gold nanoparticles. A 0.5 mm diameter laser pulse excites over a million nanoparticles. The effect of a single laser pulse on solid water doped with HCl is studied using isotope exchange to probe acidity.