Visualizing Ultrafast Chemical Reaction Dynamics

在化学系化学结构，动力学和机制-A（CSDM-A）计划的支持下，密歇根大学的Roseanne Sension和James Penner-Hahn教授正在结合先进的可见光和X射线激光方法来观察原子和电子在化学键的形成和断裂过程中的运动。化学反应是由原子和电子在万亿分之一秒或更短的时间尺度上的耦合运动控制的。普通的相机无法捕捉到这种运动。Sension和Penner-Hahn教授及其学生将使用非常短的X射线脉冲来成像光化学反应中原子和电子的耦合运动，每次聚焦一个元素。他们的发现可能会导致设计出更有效的化学品，用于从光选择性药物输送到工业上重要的光催化剂等应用。该项目还将通过培训一批不同的研究生和本科生在x射线物理学、光学、化学动力学和无机化学的界面上工作，为教育和人力资源开发做出贡献。 化学反应涉及原子排列、电子分布和成键的变化。教授Sension和Penner-Hahn联合收割机结合超快光谱和X射线光谱的优势，可视化，描述和控制这些动态。通过使用光来引发反应，分子行为可以同步，允许研究从阿秒（电子重排）到飞秒和皮秒（原子运动）的时间尺度。偏振和时间分辨X射线光谱将提供化学反应动力学的元素特定视图，补充和扩展光学和振动光谱提供的视图。研究结果可能会挑战传统思维，发现新现象，并推翻以前的模型。 在这个项目中，Sension和Penner-Hahn教授及其学生将专注于含过渡金属系统的超快相干动力学，包括有机钴络合物，这些系统驱动生物学相关的转化和技术上重要的分子转化，以及光驱动的多烯构象变化，这些变化是从视觉到分子马达的过程的基础。 超快X射线光谱适用于运输、能量收集、能量存储和生物系统中的广泛系统。这项工作的更广泛影响包括开发方法，使时间分辨X射线光谱在化学界的更广泛使用。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program in the Division of Chemistry, Professors Roseanne Sension and James Penner-Hahn of the University of Michigan are combining advanced visible and x-ray laser methods to watch the movement of atoms and electrons during the making and breaking of chemical bonds. Chemical reactions are controlled by the coupled motions of atoms and electrons on time scales measured in trillionths of a second or shorter. No ordinary camera can capture this movement. Professors Sension and Penner-Hahn and their students will use very short x-ray pulses to image the coupled motions of atoms and electrons in photochemical reactions, focusing on one element at a time. Their discoveries could lead to the design of more efficient chemicals used in applications ranging from photo-selective drug delivery to industrially important photocatalysts. This project will also contribute to education and human resource development by training a diverse group of graduate and undergraduate students to work at the interface of x-ray physics, optics, chemical dynamics, and inorganic chemistry. Chemical reactions involve changes in atomic arrangement, electron distribution, and bonding. Professors Sension and Penner-Hahn combine strengths in ultrafast spectroscopy and x-ray spectroscopy to visualize, describe, and control these dynamics. By using light to initiate reactions, the molecular behavior can be synchronized, allowing studies on time scales ranging from attoseconds, for electronic rearrangements, to femtoseconds and picoseconds for atomic motion. Polarization and time-resolved x-ray spectroscopies will provide an element specific view of chemical reaction dynamics, complementing and extending the view provided by optical and vibrational spectroscopies. The results could challenge conventional thinking, identify new phenomena, and overturn previous models. In this project Professors Sension and Penner-Hahn and their students will focus on the ultrafast coherent dynamics of transition metal containing systems, including organocobalt complexes, that drive both biologically relevant transformations and technologically important molecular conversions, as well as the light-driven conformational changes in polyenes that underlie processes ranging from vision to molecular motors. Ultrafast x-ray spectroscopies are applicable to a broad range of systems active in transport, energy harvesting, energy storage and biological systems. The broader impacts of this work include the development of methods that enable a wider use of time-resolved x-ray spectroscopies in the chemical community.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.