Negative Ion Photoelectron Spectroscopy of Atomic, Molecular and Cluster Anions

在化学系化学结构、动力学和机理A （CSDM-A）项目的支持下，约翰霍普金斯大学的Kit Bowen教授和他的团队正在研究当一个额外的电子附着在原子、分子或簇上时形成的负离子。在化学系统中加入电子可以使意想不到的事情发生，使看似不可能的过程发生。例如，电子驱动、引导、诱导和启动各种惊人的转化，包括DNA损伤、质子转移、分子激活和大量的电化学反应。电子附着产生的负离子也是化学反应机制的重要参与者，在有机化学、电化学和辐射生物学中发挥着关键作用。电子影响过程在复杂环境中是普遍存在的。由于这些原因，对涉及多余电子的基本现象的微观理解是必不可少的。为了探究这些现象，Bowen博士和他的团队使用了一种叫做负离子光电子能谱的技术来测量电子与带负电荷的原子、分子和簇的紧密程度。这些实验揭示了离子及其中性对应物的详细信息，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，Bowen博士实验室的工作具有跨学科的吸引力，其影响范围涉及大气化学，催化，辐射化学和生物学，天体化学和质谱学等各个领域。Bowen博士的工作还为教育和人力资源开发做出了巨大贡献，他指导研究生成为未来的科学家，为约翰霍普金斯大学和其他学院和大学的本科生提供参与尖端研究的机会，并为高中、初中和小学的学生提供了了解科学研究的机会。这些拓展工作鼓励那些在科学领域未被充分代表的群体参与进来。Bowen的研究考察了电子诱导质子转移（EIPT）反应，原子和分子的弱束缚（扩散）多余电子状态，以及瞬态分子阴离子的性质。例如，研究小组正在探索EIPT在簇阴离子中的作用，他们期望内部相互作用由多余的电子控制。EIPT是一个广泛传播的，甚至可能无处不在的电子辅助过程。该团队还研究了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。鲍恩博士对弱束缚（漫射）过剩电子态的研究考察了化学中一些最微妙的相互作用；在电子和原子或分子之间。在这方面，研究小组正在研究氙原子簇阴离子和巴克敏斯特富勒烯基态阴离子中极化束缚电子的形成和表征；电子亚稳原子金属阴离子中的四极束缚电子以及金属-氨簇阴离子中的多个里德伯电子。虽然电子在这两种情况下的束缚都很弱，但它们代表了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Bowen博士开发的一种独特方法研究瞬态分子阴离子，该方法将Rydberg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阴离子。他们还使用ret - ape来探索很少被研究，但却非常重要的Penning电子分离过程。这些研究促进了对电子损伤DNA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高能气体环境（如火焰和太阳大气）中阴离子的碰撞破坏过程的更深入理解。这个广泛的研究项目的成果预计将在许多科学领域产生广泛的影响。此外，该项目为研究生和本科生提供高级培训机会，同时也通过Bowen博士的外展活动吸引K-12学生。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。

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.