Ultrafast Electronic Decoherence Dynamics in Molecules

在这个项目中，研究人员将在几飞秒的时间尺度上研究电离分子内电子（电荷动力学）的运动（一飞秒是十亿分之一秒的百万分之一）。了解和控制分子中的超快电荷动力学对于生物化学过程和分子级电子器件的发展具有重要的基础意义。研究小组将使用不同波长的飞秒激光脉冲来跟踪电荷的运动，并深入了解影响电荷运动的物理机制。该项目的研究结果将为控制分子电荷动力学铺平道路，这对设计激光控制的化学反应和合成量子材料和器件具有重要意义。为了充分发挥这一潜力，一支训练有素的STEM员工队伍至关重要。作为该项目的一部分，一群不同的研究生和本科生将接受超快光子科学和量子科学方面的培训。详细了解电子激发分子中的各种退相干/消相过程对于开发用于激光驱动分子过程控制的量子相干控制协议至关重要。这在分子离子中尤其重要，因为飞秒和阿秒电荷迁移动力学在生物化学过程和电荷传输现象中具有重要意义，因此正受到密切研究。当在分子中产生带宽为几个电子伏特的多个离子态叠加时，可以启动电子相关驱动的电荷迁移动力学。了解电荷迁移过程中的电子退相干机制是实现分子超快电荷动力学控制的关键的第一步。虽然先前的许多理论和实验研究已经利用光电离探针探索了电荷迁移，但这种动力学的非线性光学探针可以提供一个全新的视角。同样，当分子在形状共振附近被光离时，暂时被困在形状共振中的电子可以影响分子离子的演化，而分子离子可能处于阳离子态的叠加状态。非线性光学测量可以探测分子离子的演化，揭示形状共振的作用。在这个项目中，研究小组将使用强场和极紫外电离分子的非线性光学测量来获得分子离子中电子退相干动力学的直接和详细信息。研究目标是：(1)在几飞秒时间尺度上研究甲基溴等分子中强场引发的电荷迁移过程中的电子退相干动力学；(2)研究形状共振对氮和二氧化碳等分子中XUV光电离后分子离子超快演化的影响。该奖项反映了美国国家科学基金会的法定使命，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, the researchers will study the motion of electrons (charge dynamics) inside ionized molecules on time scales of a few femtoseconds (one femtosecond is a millionth of a billionth of a second). Understanding and controlling ultrafast charge dynamics in molecules is of fundamental importance in biochemical processes and the development of molecular scale electronic devices. The research group will use femtosecond laser pulses of various wavelengths to track the motion of the charge and obtain insight into the physical mechanisms that influence it. The results of this project will pave the path towards control of molecular charge dynamics, which is important for the design of laser-controlled chemical reactions and synthesis of quantum materials and devices. To fully realize this potential, a highly trained STEM workforce is essential. As part of this project, a diverse group of graduate and undergraduate students will be trained in ultrafast photon science and quantum science. A detailed understanding of various decoherence/dephasing processes in electronically excited molecules is essential for the development of quantum coherent control protocols for the laser driven control of molecular processes. This is particularly important in molecular ions in which femtosecond and attosecond charge migration dynamics are being intensely studied due to their importance in biochemical processes and charge transport phenomena. When a superposition of multiple ionic states with bandwidth of a few electron volts is created in molecules, electron correlation driven charge migration dynamics can be initiated. Understanding electronic decoherence mechanisms during charge migration is a critical first step towards achieving control of ultrafast charge dynamics in molecules. While multiple previous theoretical and experimental studies have explored charge migration using photoionization probes, nonlinear optical probes of such dynamics can offer a completely novel perspective. Similarly, when molecules are photoionized near shape resonances, the electron temporarily trapped in a shape resonance can affect the evolution of the molecular ion that may be left in a superposition of cationic states. A nonlinear optical measurement can probe the evolution of the molecular ion and shed light on the role played by the shape resonance. In this project, the research group will use nonlinear optical measurements of strong-field and extreme-ultraviolet ionized molecules to obtain direct and detailed information about electronic decoherence dynamics in molecular ions. The objectives are to (1) study electronic decoherence dynamics during strong-field initiated charge migration in molecules such as methyl bromide on few-femtosecond time scales and (2) study the effect of shape resonances on the ultrafast evolution of a molecular ion after XUV photoionization in molecules such as nitrogen and carbon dioxide.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.