Collaborative Research: Probing Attosecond Dynamics in Atoms and Molecules

识别、标记和明确跟踪分子系统中电子的量子轨迹的能力是解决问题的核心，这些问题是解锁解决一系列当代科学和技术挑战的关键-了解星际介质的化学、减少我们的碳足迹、实现高效、清洁的能源和控制生物分子的动力学只是几个例子。例如，光生电荷动力学在催化、光合作用、光伏效应、生物分子中的辐射损伤和大气化学中普遍存在。在时钟速度为1飞秒(10^-15 S)的情况下，电子和原子核之间的能量流动和关联舞蹈需要亚飞秒的时间分辨率(例如，100阿秒=0.1飞秒)和精心设计的实验技术来可靠地跟踪。中佛罗里达大学(UCF)和马里兰大学(UMD)的合作已经组装了仪器和人员来研究重要原型分子的这种动力学。具体地说，电荷动力学将通过碳原子所谓的核能级状态(离原子核最近的状态)吸收光谱的瞬时变化来进行实验探索。这些新的测量可能会导致对关键物理概念的新理解，对基本过程的更清晰的描述，以及控制电子动力学的新方法。中佛罗里达大学(UCF)和马里兰大学(UMD)合作，在水窗口(在本研究中为240至330 eV)使用几个周期的红外强(IR)泵浦和阿秒软X射线探测器来瞬时吸收核心级碳原子，正在研究两个重要碳氢化合物的超快动力学。其中一组实验致力于跟踪甲烷中红外脉冲导致的结构变化，因为它失去了时间分辨率为亚飞秒的氢原子(去质子化)。第二个研究集中在红外诱导乙炔异构化为乙烯的研究上，也是以亚飞秒分辨率进行的。这些研究的一个新奇之处在于，与之前在水窗口的瞬时吸收测量相比，时间分辨率提高了40倍。UCF-UMD合作非常适合进行这项研究，因为研究人员在建造和操作最先进的阿秒激光器(UCF)以及探测和控制原子和分子动力学(UMD)方面有着悠久的历史。为了确保对实验结果的最佳解释，该团队与运行当代数字代码(如XCHEM和MESA)的UCF理论家密切合作，以帮助分析数据。这一结果将提供对强外部扰动引起的与时间相关的结构变化和相关电子运动的新见解，这可能会揭示控制电子动力学的创新方法。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。

An ability to identify, tag and follow unambiguously quantum trajectories of electrons in molecular systems is central to addressing questions that are key to unlocking solutions to an array of contemporary scientific and technical challenges - understanding the chemistry of interstellar media, reducing our carbon footprint, enabling efficient, clean energy sources and controlling dynamics in biological molecules are just a few examples. Light-induced charge dynamics, for example, is ubiquitous in catalysis, photosynthesis, the photovoltaic effect, radiation damage in biomolecules and atmospheric chemistry. With clock speeds of order 1 femtosecond (10^-15 s), the energy flow and correlated dance between electrons and atomic nuclei require subfemtosecond temporal resolution (e.g., 100 attosecond = 0.1 femtosecond) and carefully-designed experimental techniques to track reliably. The University of Central Florida (UCF) - University of Maryland (UMD) collaboration has assembled the instrumentation and personnel to study such dynamics in important prototype molecules. Specifically, charge dynamics will be probed experimentally by transient changes in the absorption spectrum of so-called core-level states (those closest to the nucleus) of the carbon atom. These novel measurements may lead to new understanding of key physical concepts, clearer pictures of fundamental processes and novel ways to control electron dynamics. Employing a few-cycle infrared intense (IR) pump and an attosecond soft X-ray probe in the water window (240 to 330 eV in this study) for transient absorption of core-level carbon atoms, the University of Central Florida (UCF) - University of Maryland (UMD) collaboration is investigating ultrafast dynamics in two important hydrocarbons. One set of experiments is dedicated to tracking structural changes induced by the IR pulse in methane as it loses hydrogen atoms (deprotonization) with subfemtosecond temporal resolution. The second study focuses on IR-induced isomerization of acetylene into vinilydene also with subfemtosecond resolution. One novelty of these studies rests in a forty-fold improvement in temporal resolution over previous transient absorption measurements in the water window. The UCF-UMD collaboration is ideally suited to carry out this investigation because of the investigators' long history in building and operating state-of-the-art attosecond lasers (UCF) and probing and controlling atomic and molecular dynamics (UMD). To ensure the best interpretation of the experimental results, the team works closely with UCF theorists running contemporary numerical codes such as XCHEM and MESA to help analyze the data. The results will provide new insight into time-dependent structure changes and correlated electron motion induced by strong external perturbation, which potentially could reveal innovative ways to control electron dynamics.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.