QLC: EAGER: Toward the visualization of chemical control

在这个由化学系化学结构动力学和机制（CSDM-A）计划资助的项目中，密歇根大学的Roseanne Sension教授正在使用X射线技术开发暴露于紫外线（UV）或可见光（维斯）脉冲的分子中原子内部运动的视觉图像和电影。 紫外/维斯光的脉冲可以导致分子中化学键的扭曲，甚至导致它们在我们所谓的光化学反应中断裂或重新形成。 这些光致运动发生在非常短的时间尺度上，从几飞秒到几纳秒（飞秒是一秒的千万亿分之一。 纳秒是十亿分之一秒）。 X射线衍射用于测定分子结构已有世纪的历史。 然而，这些分子在晶格中是固定的。 为了捕捉分子在暴露于光后的极快运动，Sensions教授正在使用自由电子激光器产生的强烈X射线（例如，在斯坦福大学的LINAC相干光源）。Sension教授和她的学生正在测量分子如何吸收X射线，并开发将X射线吸收信息转换为图像的方法，这些图像可以作为电影中的帧进行排序。 在分子水平上对光化学反应进行可视化，有助于我们理解一般的化学反应，也有助于实现用光控制化学反应的长期目标。该项目还在培训学生使用先进的实验设施和先进的计算机模拟紫外/维斯光和X射线吸收。 此外，研究结果正在被整合到本科课程中，以帮助学生理解数学和物理与化学的相关性。该项目使用飞秒x射线自由电子激光器来可视化分子中的量子波包运动。短激光脉冲用于引发和控制光化学反应。极化的X射线脉冲探测激发态势能面上的相干结构动力学。钴胺素光化学和光物理被用作飞秒X射线脉冲源的分子可视化和量子控制的模型系统。相干激发态动力学的可视化和与分子配体的动力学的相关性促进了对基于钴胺素的分子器件的理解和发展。用量子化学计算和有限差分近边光谱从头算程序模拟X射线吸收光谱解释了实验观测结果。此外，一般的模拟方法正在开发模型超快X射线光谱和相干激发态动力学。 该研究项目在能量转换、医疗治疗、分子电子学、开关、传感器和输送平台等领域具有广泛的应用前景。该奖项反映了NSF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 Roseanne Sension of The University of Michigan is using x-ray techniques to develop visual images and movies of the internal motions of the atoms in molecules which have been exposed to a pulse of ultraviolet (UV) or visible (Vis) light. Pulses of UV/Vis light can cause distortions of the chemical bonds in molecules, and even cause them to break or re-form in what we call a photochemical reaction. These light-induced motions occur on very short time scales, from a few femtoseconds to a few nanoseconds (A femtosecond is one quadrillionth of a second. A nanosecond is one billionth of a second). X-ray diffraction has been used to determine molecular structure for more than a century. However, these have been molecules that are stationary in a crystal lattice. In order to capture the extremely fast motions of molecules after they have been exposed to light, Prof. Sensions is using the intense x-rays produced by free electron lasers (for example, at the LINAC Coherent Light Source at Stanford University). Professor Sension and her students are measuring how molecules absorb x-rays, and developing methods to convert x-ray absorption information into images that can be sequenced as frames in a motion picture. The visualization of photochemical reactions at the molecular level helps us understand chemical reactions in general, and also supports the long-term goal to control chemical reactions with light. The project is also training students in the use of advanced experimental facilities and in advanced computer simulation of UV/Vis and x-ray absorption. In addition, the results are being integrated into the undergraduate curriculum to help students understand the relevance of mathematics and physics to chemistry.This project uses femtosecond x-ray free electron lasers to visualize quantum wave packet motion in molecules. A short laser pulse is used to initiate and control a photochemical reaction. A polarized x-ray pulse probes the coherent structural dynamics on the excited state potential energy surface. Cobalamin photochemistry and photophysics is used as a model system for molecular visualization and quantum control with femtosecond x-ray pulses sources. The visualization of coherent excited state dynamics and the correlation of dynamics with the molecular ligands facilitate the understanding and development of cobalamin based molecular devices. The experimental observations are interpreted using quantum chemical calculations and finite difference near edge spectroscopy ab initio code to simulate x-ray absorption spectra. In addition, general simulation methods are being developed to model ultrafast x-ray spectroscopy and coherent excited state dynamics. This research project has implications for a wide range of applications in energy conversion, medical therapeutics, molecular electronics, switches, sensors, and delivery platforms. Many of these applications exploit intrinsically quantum mechanical dynamics of the molecules involved.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.