Electron-driven Correlated Dynamics of Complex Systems

电子-分子相互作用启动和驱动了几乎所有与辐射损伤、环境化学、微电子材料加工和现代照明应用中使用的工业等离子体等领域相关的化学过程。最近，人们也越来越多地意识到电子-分子相互作用在生物系统中的重要性。例如，由于电离辐射通过生物材料，低能电子似乎在驱动DNA链断裂方面有显著影响。鉴于电子-分子相互作用在许多环境中的重要性，我们必须了解电子相互作用如何驱动化学过程，特别是那些导致分子中键断裂的过程，因为剩余的碎片往往是化学反应和反应链的先驱。理解能量如何流入和流出分子系统也很重要。正是这种能量流支配着任何电子-分子相互作用的动力学。鉴于现代计算资源的进步，理论模型有望解决电子与更复杂系统的相互作用，即那些超过两个或三个原子的系统。然而，由于作为基准的实验测量的稀疏性，很难对这些模型的结果赋予任何程度的置信度。这个项目将测量几个复杂的分子系统，例如碳氢化合物、醇和简单的有机分子，在电子相互作用中驱动的键断裂和分子动力学，作为理论模型的实验基准。电子与上述复杂系统的相互作用揭示了当驱动到非平衡状态时的结构和动力学信息。通过探索高能和低能电子与这些复杂系统的相互作用，我们可以确定更深入地理解驱动关联动力学的物理机制。该项目将奥本大学的动量碎片成像仪应用于电子-分子相互作用的关联动力学研究。动量成像技术测量由于电子相互作用而产生的解离碎片离子的全三维动量。这允许完全研究作为电子能量和相对于键轴的相互作用角的函数的解离动力学。它还可以测量解离碎片离子的平动能和内旋振动能之间的能量分配。在低电子能量下，解离电子附着(DEA)依赖于电子相对于特定键轴的入射角，可以实现键断裂的选择性。DEA的最新结果表明，除了准双原子表示外，必须考虑复杂的伸缩和弯曲动力学，以充分解释三原子体系的解离动力学。该项目将通过过渡到更复杂的系统来扩展以前的工作，如上所述，这些系统以前很少或根本没有实验关注。在较高的电子能量下，还将通过解离电离和离子对过程形成的离子的动量成像来探索被驱动到高激发态和离子态的选定的双原子和三原子系统的结构和动力学。在低能和高能状态下，这些不同的过程都表现出恒定的能量传递。正是这种恒定的能量转移允许对这些过程中涉及的状态进行具体确定。

Electron-molecule interactions initiate and drive almost all chemical processes relevant to areas such as radiation damage, environmental chemistry, industrial plasmas used in the processing of materials for microelectronics and in modern lighting applications. Recently, there has also been an increasing awareness of the importance of electron-molecule interactions in biological systems. For example, low-energy electrons seem to have a significant effect in driving DNA strand breaks due to the passage of ionizing radiation through biological material. Given the prominence of electron-molecule interactions in many environments, it is imperative that we understand how electron interactions drive chemical processes, particularly those that lead to bond breaking in molecules, as the remaining fragments often serve as progenitors to chemical reactions and reaction chains. It is also important to understand how energy flows into and out of molecular systems. It is this energy flow that governs the dynamics of any electron-molecule interaction. Given advancements in modern computational resources, theoretical models are poised to address electron interactions with more complex systems, that is, those of more that two or three atoms. However it is difficult to assign any level of confidence to the outcomes of these models due to the sparsity of experimental measurements to benchmark against. This project will measure the bond breaking and molecular dynamics driven in electron interactions with several complex molecular systems, for example, hydrocarbons, alcohols, and simple organic molecules, to serve as experimental benchmarks to theoretical models.The interactions of electrons with the complex systems above reveal information about the structure and dynamics when driven to non-equilibrium states. By exploring both high- and low-energy electron interactions, with these complex systems, we can ascertain a more in-depth understanding of the physics driving the correlated dynamics. This project brings the application of the momentum fragment imaging apparatus at Auburn University to the study of correlated dynamics in electron-molecule interactions. The momentum imaging technique measures the full three-dimensional momentum of dissociation fragment ions as a result of electron interaction. This allows for a complete study of dissociation dynamics as a function of both electron energy and interaction angle with respect to a bond axis. It also allows for a measurement of the energy partitioning between translational and internal ro-vibrational energy of dissociating fragment ions. At low electron energies, dissociative electron attachment (DEA) is dependent on the incidence angles of electrons, with respect to particular bond axes, and selectivity of bond cleavage can be realized. Recent results for DEA show that complex stretching and bending dynamics, beyond a quasi-diatomic representation, must be accounted for to adequately explain the dissociation dynamics of triatomic systems. This project will extend previous work by transitioning to more complex systems, as mentioned above, that have seen little or no previous experimental attention. At higher electron energies, the structure and dynamics of select diatomic and triatomic systems driven into highly excited and ionic states will also be probed via momentum imaging of ions formed by the dissociative ionization and ion-pair processes. At both the low- and high-energy regimes, these various processes exhibit constant energy transfer. It is this constant energy transfer that allows for the specific determination of states involved in these processes.