A Deep Dive into Electron-Neutral Interactions

在这个由化学部门化学结构动力学和机制（CSDM-A）项目资助的项目中，印第安纳大学的Caroline Chick Jarrold教授和她的学生正在使用几种复杂的实验技术研究电子和中性分子之间的相互作用，这些实验技术是基于所研究的化合物对光的吸收和发射。电子-中性相互作用驱动许多重要的化学和物理过程，但它们很难通过实验来探索。从实际的角度来看，控制电子是具有挑战性的，因为它们比原子轻数千倍，而原子本身就是微小的粒子，同时，电子所携带的电荷使其容易受到地球磁场的偏转，以及实验室环境中存在的其他弱作用力的影响。Jarrold教授克服了这些障碍，他以一种可控的方式制备自由电子，即用激光脉冲去除一个已知能量的电子，并在理想的中性目标分子附近瞄准带负电荷的分子。选择用于研究的分子阵列是为了对影响其与电子相互作用的广泛性质进行采样。实验涉及光电子作为探测分子和双分子复合物的价键、非价键和临时阴离子状态的工具的新用途，重点是制备和探测不完全属于这三类的系统。该项目提出了几个假设，涉及电子驱动化学的描述，电子-生物分子相互作用的日益复杂的景观，以及控制非价键阴离子寿命的规则。用能量选择电子对这些系统进行实验探测是通过分离阴离子前体来实现的，这为绘制电子-中性相互作用的能量依赖性提供了一条途径，其中一些相互作用引发了电子驱动化学。其他研究包括荧光寿命和分散荧光测量阴离子的非价键激发态。合作者、东南路易斯安那大学的Thomas Sommerfeld教授在阴离子非价态的理论处理方面具有专业知识，他对收集到的这些复杂且经常短暂的物种的数据进行了解释，并进行了计算。更广泛的影响包括更全面地了解电子驱动的化学和物理过程，这是控制这些过程的先决条件。此外，该项目的参与者将在一个致力于多样性和公平性的PI实验室接受全面的化学物理技术的研究生或博士后培训，以及充足的专业发展机会。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。

In this project, funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Caroline Chick Jarrold and her students at Indiana University are studying interactions between electrons and neutral molecules using several sophisticated experimental techniques that are based on the absorption and emission of light by the chemical compounds being studied. Electron-neutral interactions drive many important chemical and physical processes, yet they are difficult to explore experimentally. From a practical standpoint, controlling electrons is challenging because they are thousands of times lighter than atoms, which themselves are tiny particles, while at the same time, the electric charge carried by the electron makes it vulnerable to deflection by the earth’s magnetic field, among other weak influencing forces present in laboratory settings. Professor Jarrold overcomes these hurdles by preparing the free electrons in a controlled way, which is to target negatively charged molecules with a laser pulse that removes an electron with a known amount of energy, and in the desired proximity of a neutral target molecule. The array of molecules selected for study are chosen to sample a broad range of properties that affect their interactions with electrons. The experiments involve the novel use of photoelectrons as a tool for probing valence-bound, non-valence-bound, and temporary anion states of molecules and bimolecular complexes, with an emphasis on preparing and probing systems that do not neatly fall into any of these three categories. This project addresses several hypotheses involving the description of electron-driven chemistry, the increasingly complex landscape for electron-bimolecular interactions, and the rules that govern non-valence-bound anion lifetimes. Probing these systems experimentally with energy-selected electrons is achieved by detachment of anionic precursors, which provides a route to mapping the energy-dependence of electron-neutral interactions, some of which initiate electron-driven chemistry. Additional studies include fluorescence lifetime and dispersed fluorescence measurements on non-valence-bound excited states of anions. Interpretation of data collected on these complex and often transient species is supported by calculations conducted by collaborator Professor Thomas Sommerfeld of Southeastern Louisiana University, who has expertise in the theoretical treatment of non-valence states of anions. The broader impacts include a more complete picture of electron-driven chemical and physical processes, which is a prerequisite for controlling these processes. In addition, participants in this project receive well-rounded graduate or postdoctoral training in a range of techniques in chemical physics, coupled with ample professional development opportunities, in the laboratory of a PI with a deep commitment to diversity and equity.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.