Photoelectron Spectroscopy of Molecular and Cluster Anions

在这个由化学系化学结构动力学和机理（CSDM-A）计划资助的项目中，约翰霍普金斯大学的Kit Bowen教授正在使用阴离子光电子能谱来研究各种分子和簇阴离子。 光电子能谱（PES）需要使用高能光（例如紫外光或X射线光）从原子、分子或固体中发射电子。 射出的电子的能量揭示了电子与分子结合的强度以及分子内化学键的类型和强度。 团簇是原子或分子的聚集体，它们通过相同的凝聚力聚集在一起，这种凝聚力是固体和液体存在的原因。分子和簇的阴离子是这些实体的带负电荷的离子（即，它们具有多于所需数量的电子）。 该项目使用PES来表征这些物种上的额外电子，因为这些额外电子可能导致其化学性质发生重大变化。 这项研究为化学键的基本性质提供了新的见解。 它也可能在其他科学领域产生影响，例如辐射生物学，肿瘤学和天体化学。参与该研究项目的研究生不仅接受PES技术培训，还接受分子结构理论方面的培训。Bowen小组正在与中学科学教师合作，帮助他们将对科学的热情带入课堂。 该小组为中小学教师和学生提供实验室图尔斯参观和课堂演示。该项目通过多种方式促进对化学和相关领域的知识和理解。(1)卤素成键在超分子化学、晶体工程和分子识别等领域有着重要的应用。本工作旨在探索阴离子络合物中的双分子卤素键合相互作用，即，在分子水平上。(2)电子诱导质子转移（EIPT）是化学和生物学中的一个基本过程。本工作的重点是羧酸和三唑之间的分子间EIPT和水合N-杂环分子内。研究了电子激发中性分子的激发态分子内质子转移（ESIPT）与基态分子阴离子的分子内EIPT之间的关系。它还探讨了分子间EIPT在卤化氢-水簇阴离子中的作用。(3)电子和分子/团簇之间存在几种不同的相互作用，导致扩散电子状态。结合可能有其根源在电子极化率，电子偶极子，或电子四极相互作用，或它可能来自相关效应单独。甚至更微妙的相互作用导致双里德伯阴离子的形成。Bowen教授的新设备结合了Rydberg电子转移和阴离子光电子能谱，作为制造和研究这些实体的工具。(4)分子活化通常是反应性的先决条件。这项工作的目的是探索在各种系统中的电子辅助分子活化过程。

In this project, funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Kit Bowen of Johns Hopkins University is using anion photoelectron spectroscopy to study a variety of molecular and cluster anions. Photoelectron spectroscopy (PES) entails the use of high energy light (for example ultraviolet or x-ray light) to eject electrons from atoms, molecules or solids. The energy of the ejected electrons reveals information about how strongly the electrons were bound to a molecule as well as the type and strength of chemical bonds within the molecule. Clusters are aggregates of atoms or molecules held together by the same cohesive forces responsible for the existence of solids and liquids. Anions of molecules and clusters are negatively-charged ions of these entities (i.e., they have more than the needed number of electrons). This project uses PES to characterize the extra electrons on these species as these extra electrons can lead to major changes in their chemical properties. This research is providing new insights into the basic nature of chemical bonds. It may also have implications in other areas of science, for example in radiation biology, oncology, and astrochemistry. Graduate students involved in this research project are receiving training not only in the PES technique but in the theoretical aspects of molecular structure. The Bowen group is working with secondary school science teachers to help bring enthusiasm for science into their classrooms. The group offers lab tours and classroom presentations for elementary and middle school teachers and students.This project contributes to knowledge and understanding in chemistry and related fields in several ways. (1) Halogen bonding plays important roles in supramolecular chemistry, crystal engineering, and molecular recognition. This work aims to explore bimolecular halogen bonding interactions in anionic complexes, i.e., at the molecular level. (2) Electron-induced proton transfer (EIPT) is a fundamental process in both chemistry and biology. This work focuses on inter-molecular EIPT among carboxylic acids and triazoles and within hydrated N-heterocyclic molecules. It investigates the relationship between excited state intra-molecular proton transfer (ESIPT) in electronically-excited neutral molecules and intra-molecular EIPT in ground state molecular anions. It also explores the role of inter-molecular EIPT in hydrogen halide-water cluster anions. (3) There are several different interactions between electrons and molecules/clusters that result in diffuse electron states. Binding may have its roots in electron-polarizability, electron-dipole, or electron-quadrupole interactions, or it may derive from correlation effects alone. Even more subtle interactions result in the formation of double Rydberg anions. Professor Bowen's new apparatus combines Rydberg electron transfer and anion photoelectron spectroscopy as a tool for making and studying these entities. (4) Molecular activation is often a prerequisite for reactivity. This work aims to explore electron-assisted molecular activation processes in a variety of systems.