Probing Coupled Electronic and Vibrational Motions in Ultrafast Proton Transfer Processes with Mixed-Frequency Multidimensional Vibronic and Soft X-ray Spectroscopies

在这项由化学系化学结构与动力学A(CSDM-A)计划资助的项目中，华盛顿大学的Munira Khalil教授正在使用先进的激光技术来了解质子(没有电子的氢原子)是如何从同一分子中的氧原子(质子供体)运动到氮原子(质子受体)的。这个过程被称为分子内(分子内)质子转移，是自然光合作用的基本步骤，也是一些能量转换过程，如从光能中产生氢燃料。一些重要的质子转移过程发生得非常快，例如，在不到200飞秒(一万亿分之一秒)的时间内。这个过程的速度很快，很难测量，也很难回答这样的问题：“分子内质子转移的速度如何取决于分子结构？”为了克服这一挑战，哈利勒教授正在设计利用各种光波长的实验工具，从红外光谱(我们感觉到的长波长波长)到X射线(非常短的波长)。这些工具提供了有关分子内电子和原子运动的详细信息。这项研究为开发更有效的将光转化为化学能的分子提供了新的信息。这项努力还创造了新的飞秒技术，并培训研究生掌握尖端光学技术。哈利勒教授开展了一项外展计划，其中包括为来自STEM弱势背景的中学女孩开设的动手光学模块。该项目是通过华盛顿大学伯克博物馆开展的“科学女孩”项目的一部分。这个研究计划的第一个目标是绘制一系列具有不同氢键强度的分子内氢键络合物中电子激发和振动运动之间的关系。第二个目标是了解分子如何在吸收光子后摆脱多余的能量(这种情况发生在DNA复合体中)，作为氢键供体和受体之间的距离和角度的函数。前两个目标是利用哈利勒教授的实验室开发的先进激光技术实现的。最终的目标是用元素特定的软X射线光谱绘制质子给体和受主位置的电子分布图。X射线实验是在劳伦斯伯克利国家实验室(加州伯克利)的高级光源(ALS)进行的。更广泛的影响包括增加对光诱导的电子-质子转移过程的了解，这是几个自然和人工能量转换过程中的重要反应，可能导致开发用于替代能源生产的新分子、材料和设备。该团队还在创造新的飞秒技术，并在实验室和X射线同步加速器上培训下一代科学家最先进的超快技术。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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 and Dynamics-A (CSDM-A) program of the Chemistry Division, Professor Munira Khalil of the University of Washington is using advanced laser techniques to understand how a proton (a hydrogen atom without its electron) moves from an oxygen atom (proton donor) to a nitrogen atom (proton acceptor) in the same molecule. This process is termed intramolecular (within the molecule) proton transfer and is a fundamental step in natural photosynthesis, as well as some energy conversion processes like hydrogen fuel generation from light energy. Some important proton transfer processes occur extremely quickly, for example in less than two hundred femtoseconds (one quadrillionth of a second). The rapidity of this process makes it difficult to measure, and to answer such questions as, "how does the speed of intramolecular proton transfer depend on the structure of the molecule?". To overcome this challenge, Professor Khalil is designing experimental tools that utilize a wide range of light wavelengths, from the infrared spectrum (long wavelengths that we feel as "heat") to X-rays (very short wavelengths). These tools provide detailed information about the motions of electrons and atoms within molecules. This research provides new information to develop more efficient molecules for converting light into chemical energy. The effort also creates new femtosecond technologies and trains graduate students in cutting-edge optical techniques. Professor Khalil conducts an outreach program that includes a hands-on optics module for middle school girls from STEM-disadvantaged backgrounds. This program is part of the "Girls on Science" program conducted through the University of Washington's Burke Museum. The first objective of this research program is to map the relationship between electronic excitation and vibrational motion in a series of intramolecular hydrogen-bonded complexes with different hydrogen bond strengths. The second objective is to understand how a molecule shakes off excess energy after absorbing a photon (this happens in DNA complexes) as a function of the distance and angle between the hydrogen bond donor and acceptor. The first two objectives are accomplished using advanced laser techniques developed in the Professor Khalil's laboratory. The final goal is to map the electron distribution at the proton donor and acceptor sites with element specific soft X-ray spectroscopy. The X-ray experiments are conducted at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory (Berkeley, CA). The broader impacts include an increased understanding of light-induced electron-proton transfer processes, which are important reactions in several natural and artificial energy conversion processes that may lead to the development of new molecules, materials and devices for alternative energy production. The team is also creating new femtosecond technologies and training the next generation of scientists in state-of-the art ultrafast techniques in the laboratory and at X-ray synchrotrons.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.