Collaborative Research: Attosecond Charge Dynamics in Atoms and Molecules

合作研究：原子和分子的阿秒电荷动力学

• 批准号: 1506345
• 负责人: Zenghu Chang
• 金额: $ 15万
• 依托单位: The University of Central Florida Board of Trustees
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-15 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1506345&HistoricalAwards=false
• 关键词: Collaborative; Research; Attosecond; Charge; Dynamics

In the late 1800s, flash photography enabled the motion of macroscopic objects to be slowed to the point where the true order of events could be extracted. Nearly a century later, femtosecond pulses (1 femtosecond is one millionth of one billionth of a second) enabled the motions of atoms to be frozen during the formation and breakup of molecules, resulting in an improved microscopic picture of chemistry. The advent of attosecond pulses, a million times shorter, allows the motion of the tiniest building block of matter, the electron, to be stopped in its tracks. Professors Chang, of the University of Central Florida, and Hill, of the University of Maryland, together with their students, use attosecond laser pulses to study electronic charge dynamics on timescales commensurate with its indigenous motion in atomic and molecular systems. Charge migration, as it is known, is central to a variety of important processes such as photosynthesis, radiation damage in biomolecules and photovoltaics used in solar panels. This collaborative project is providing insight into the collective and interactive motion of electrons that are ubiquitous in atoms, molecules and solids. An improved understanding of charge migration will have broad application from controlling the flow of energy within a molecule to tailoring the performance of materials to specific needs.Photoinduced charge separation in molecules is the first step in many chemical processes and central to our understanding of electron correlation and the energy exchange between electronic and nuclear motion responsible for catalysis, photosynthesis, photovoltaics and radiation damage in biomolecules. Comprehensive numerical simulations of complex molecules predict that when an electron is 'suddenly' removed from one end of a chain molecule, such as a small peptide, the hole can move to the other end of the molecule in less than 10 fs, before the electron-nuclear coupling takes place. Intense, isolated attosecond pulses are required to study this naturally-occurring charge migration. Professors Chang and Hill, in a collaborative project between the University of Central Florida (UCF) and the University of Maryland (UMD), exploit the attosecond source at UCF to investigate charge migration in multi-electron atoms (He) and multi-atom molecules (SO2) via attosecond pump - attosecond probe experiments. The pump pulse initiates rapid excitation (in the absence of nuclear motion in the molecular case) while the probe pulse monitors the ensuing charge migration. Two probe techniques are used to 'watch' the charge migration: transient absorption and photoelectron angular distribution. In distinction with previous attosecond studies, where charge migration was investigated in the presence of a strong external infrared field, the UCF-UMD study is probing charge migration subsequent to excitation but in the absence of any external perturbation. As a consequence, this project is providing a clearer understanding of charge separation, energy flow and electron-nuclear charge coupling, which, as stated above, are relevant to a variety of processes associated with chemical reactions, dynamics in condensed matter systems and biological phenomena. A secondary goal of this project is the development of general experimental tools that can be transferred to more complicated systems, such as ABCU (1-azabicyclo [3.3.3] undecane), for which theoretical predictions exist and the excitation spectra fall near those of the model systems of this study.

在1800年代后期，Flash摄影使宏观对象的运动得以减慢到可以提取事件的真实顺序的程度。 近一个世纪后，飞秒脉冲（1秒秒为1000亿秒的十亿个脉冲）使原子的运动在分子的形成和分解过程中得以冻结，从而改善了化学的显微镜图。 Attsond脉冲的出现，短次，使最小的问题（电子构件）的运动可以在其轨道上停止。 佛罗里达大学中央大学和马里兰州大学的Hill教授以及他们的学生一起使用Attosond激光脉冲研究与原子和分子系统中的土著运动的时尺度上的电子电荷动力学。 众所周知，电荷迁移是各种重要过程的核心，例如光合作用，生物分子中的辐射损伤和太阳能电池板中使用的光伏。 这个协作项目正在提供有关原子，分子和固体无处不在的电子的集体和互动运动的见解。 对电荷迁移的深入了解将从控制分子内的能量流到将材料的性能定制到特定需求。分子中的电荷分离是许多化学过程中的第一步，是我们对电子相关性以及对电子相关性的理解以及对电子和核运动负责催化性，光电效应，光电量，放射损害的损害的第一步。 复杂分子的综合数值模拟预测，当电子从链分子的一端“突然”“突然”（例如小肽）“突然”去除时，在发生电子核偶联之前，该孔可以在小于10 fs的另一端移至分子的另一端。 需要强烈的，孤立的Attosond脉冲来研究这种自然发生的电荷迁移。 Chang and Hill教授在中央佛罗里达大学（UCF）和马里兰大学（UMD）之间的合作项目中，利用UCF的Attosend Source通过Attosond Pump-Attosecond pump-attosecond probe probe实验来调查多电子原子（HE）和多原子分子（SO2）中的电荷迁移。 泵脉冲会引发快速激发（在分子情况下没有核运动的情况下），而探针脉冲则监测随后的电荷迁移。 两种探针技术用于“观察”电荷迁移：瞬态吸收和光电子角分布。 与以前的Attosond研究区别，在存在强大的外部红外领域的情况下研究了电荷迁移，UCF-UMD研究正在探测激发后的电荷迁移，但没有任何外部扰动。 结果，该项目提供了对电荷分离，能量流量和电子核电电荷耦合的更清晰的理解，如上所述，这与与化学反应，凝结物质系统中的动态和生物学现象相关的各种过程有关。 该项目的次要目标是开发一般的实验工具，这些工具可以转移到更复杂的系统，例如ABCU（1- azabicyclo [3.3.3] undecane），为此存在理论预测，激发光谱落在了本研究模型系统的附近。