Negative Ion Photoelectron Spectroscopy of Atomic, Molecular and Cluster Anions

在化学系化学结构、动力学和机制A(CSDM-A)计划的支持下，约翰霍普金斯大学的Kit Bowen教授和他的团队正在研究当额外的电子连接到原子、分子或团簇时形成的负离子。向化学体系中添加电子可以使意想不到的事情发生，诱使似乎不可能发生的过程发生。例如，电子驱动、引导、诱导和启动了各种惊人的转变，包括DNA损伤、质子转移、分子激活和大量的电化学反应。电子结合产生的负离子也是化学反应机制中的关键因素，在有机化学、电化学和辐射生物学中发挥着关键作用。在复杂的环境中，受电子影响的过程是普遍存在的。出于这些原因，对涉及过剩电子的基本现象的微观理解是至关重要的。为了探索这些现象，鲍恩博士和他的团队使用一种名为负离子光电子能谱的技术来测量电子与带负电荷的原子、分子和团簇的结合有多紧密。这些实验揭示了关于离子和它们的中性对应离子的详细信息，同时也为计算化学提供了重要的基准。考虑到电子驱动过程的广泛重要性，鲍恩博士实验室的工作具有跨学科的吸引力，影响涉及大气化学、催化、辐射化学和生物学、天体化学和质谱学等多个领域。鲍恩博士的工作还为教育和人力资源开发做出了巨大贡献，他指导了未来将成为科学家的研究生，为约翰·霍普金斯大学和其他学院和大学的本科生提供了参与尖端研究的机会，并让高中、初中和小学生得以一窥科学研究。外展努力鼓励在科学界代表性不足的群体参与。鲍恩的研究考察了电子诱导的质子转移(EIPT)反应、原子和分子的弱结合(扩散)过剩电子态，以及瞬时分子阴离子的性质。例如，研究小组正在探索EIPT在团簇阴离子中的作用，他们预计内部相互作用将由过剩电子控制。EIPT是一种广泛的，甚至是无处不在的电子辅助过程。该团队还在研究基态分子阴离子中的EIPT与中性分子中激发态分子内质子转移(ESIPT)过程之间的关系。鲍恩博士对弱结合(扩散)过剩电子态的研究考察了化学中一些最微妙的相互作用，即电子与原子或分子之间的相互作用。在这一领域，研究小组正在研究氙原子团簇阴离子和巴克明斯特富勒烯基态阴离子中可极化束缚电子的形成和表征；电子亚稳原子金属阴离子中四极束缚电子的形成和表征；以及金属氨团簇阴离子中多里德堡电子的形成和表征。尽管在每一种情况下，电子都是弱束缚的，但它们代表着相互作用逐渐增强的阶梯上的台阶。最后，研究小组正在使用由Bowen博士开发的一种独特的方法来研究瞬时分子阴离子，该方法将里德伯格电子转移与阴离子光电子能谱(RET-APES)相结合。研究小组使用RET-APES技术来形成和表征核碱基分子、Criegee中间体和碘化氢分子的价态阴离子。他们还在使用RET-APES探索鲜为人知但却是根本重要的彭宁电子分离过程。这些研究有助于更深入地了解电子对DNA损伤的最早阶段、重要大气中间体的亲电性质、HI阴离子的意外稳定性以及在高能气体环境中(如火焰和太阳大气)的碰撞阴离子破坏过程。这一广泛的研究项目的结果预计将在许多科学领域产生广泛影响。此外，该项目为研究生和本科生提供高级培训机会，同时通过Bowen博士的外展活动吸引K-12学生。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) Program in the Division of Chemistry, Professor Kit Bowen and his group at Johns Hopkins University are studying the negative ions that form when an extra electron is attached to an atom, molecule, or cluster. The addition of electrons to chemical systems can make the unexpected occur, enticing seemingly impossible processes to take place. For example, electrons drive, direct, induce, and initiate an astonishing variety of transformations, including DNA damage, proton transfer, molecular activation, and a vast array of electrochemical reactions. The negative ions that result from electron attachment are also crucial actors in chemical reaction mechanisms, playing key roles in organic chemistry, electrochemistry, and radiation biology. Electron-influenced processes in complex environments are ubiquitous. For these reasons, a microscopic understanding of basic phenomena involving excess electrons is essential. To probe these phenomena, Dr. Bowen and his group use a technique called negative ion photoelectron spectroscopy to measure how tightly electrons are bound to negatively charged atoms, molecules, and clusters. The experiments reveal detailed information about both the ions and their neutral counterparts, while also providing important benchmarks for computational chemistry. Considering the wide-ranging importance of electron-driven processes, the work in Dr. Bowen’s lab has interdisciplinary appeal, with impact ranging across fields as diverse as atmospheric chemistry, catalysis, radiation chemistry and biology, astrochemistry, and mass spectrometry. Dr. Bowen’s work also makes strong contributions to education and human resource development by mentoring graduate students who will become the scientists of tomorrow, by providing undergraduates from Johns Hopkins and other colleges and universities an opportunity to participate in cutting-edge research, and by giving high school, middle school, and elementary school students a glimpse into scientific research. The outreach efforts encourage participation from groups that are underrepresented in science.Dr. Bowen’s research examines electron-induced proton transfer (EIPT) reactions, weakly-bound (diffuse) excess electron states of atoms and molecules, and the properties of transient molecular anions. For example, the research team is exploring the role of EIPT in cluster anions, where they expect the internal interactions to be governed by the excess electron. EIPT is a wide-spread, perhaps even ubiquitous electron-assisted process. The team is also examining the relationship between EIPT in ground-state molecular anions and the process of excited-state intra-molecular proton transfer (ESIPT) in neutral molecules. Dr. Bowen’s research on weakly-bound (diffuse) excess electron states examines some of the most subtle interactions in chemistry; those between electrons and atoms or molecules. In this area, the research team is studying the formation and characterization of polarizability-bound electrons in xenon atomic cluster anions and in ground state anions of buckminsterfullerene; quadrupole-bound electrons in electronically metastable atomic metal anions; and multiple Rydberg electrons in metal-ammonia cluster anions. Although the electrons are weakly bound in each of these cases, they represent steps on a staircase of progressively stronger interactions. Finally, the research team is studying transient molecular anions using a unique approach, developed by Dr. Bowen, that combines Rydberg electron transfer with anion photoelectron spectroscopy (RET-aPES). The research team uses the RET-aPES technique to form and characterize valence anions of nucleobase molecules, the Criegee intermediate, and the hydrogen iodide molecule. They are also using RET-aPES to explore the barely studied, yet fundamentally important process of Penning electron detachment. These studies foster a deeper understanding of the earliest stages of electron damage to DNA, the electrophilic properties of important atmospheric intermediates, the unexpected stability of HI anion, and collisional anion destruction processes in energetic gaseous environments, such as flames and solar atmospheres. The outcomes from this broad research project are expected to have widespread impact across many fields of science. Additionally, the project provides advanced training opportunities for graduate and undergraduate research students, while also engaging K-12 students through Dr. Bowen's outreach activities.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.