CAREER: Photo-induced Ultrafast Electron-nuclear Dynamics in Molecules

摘要：当一个分子受到突然的扰动，例如一个或多个电子被移除时，剩余的电子和原子核就会移动。在许多情况下，人们可以假设，随着分子形状的改变，轻电子会立即适应重原子核的位置（“玻恩-奥本海默近似”），但这只是近似正确的。电子既具有波的性质又具有粒子的性质，它们可以相互干扰。与原子核的运动相比，由此产生的电子波包可以快速振荡。这种“电子相干”被认为在视觉等化学和生物过程中很重要，但由于它们进化的时间尺度极短（几阿秒，其中一阿秒= 0.000000000000000001秒），因此很难研究。这种极快的电子运动将受到原子核相对较慢的运动的影响。PI和她的研究团队将在中佛罗里达大学校园内使用最先进的激光和光子源来研究这些电子相干的演变及其与潜在核运动的耦合。最终，这些研究可能会提高我们设计反应产物和优化能量收集的能力。该职业奖支持本科生、研究生和博士后研究人员，他们将接受使用最先进的激光系统和相关的先进光谱技术的培训。此外，该奖项还支持一个教育和推广项目，其中包括一个针对学生的仪器培训暑期项目，一个面向更广泛受众的超快科学入门视频序列，以及为高中教师和学生举办的名为“Go ultrafast !”的活动。摘要：当相干光与分子相互作用时，多个电子态可以被特定的相对相填充，从而产生电子相干。在这个项目中，这些电子相干的演变将在电子和离子运动的自然时间尺度上具有时间分辨率的泵浦探针方案中进行时间分辨。电子-核耦合对电子相干特性的影响，如它们的长度、强度和恢复，将被研究。飞秒红外/近红外激光器和阿秒XUV/x射线桌面光源将被用作泵浦或探头。电子相干将通过电子动能和丰度变化作为泵浦-探针延迟的函数来监测，使用三维动量成像和瞬态吸收光谱的电子-离子光谱。同时测量动量空间中的电子和离子，以显示电子动力学演化与离子运动之间的相关性。该项目将促进我们对分子中电荷动力学和光能转换和转移机制的理解，并为指导能量流动的光控制方案铺平道路。研究结果将为非玻恩-奥本海默体系理论方法的验证提供可靠的参考。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。

General audience abstract: When a molecule is subject to a sudden disturbance, such as the removal of one or more electrons, the remaining electrons and atomic nuclei move. In many cases, one can assume that the light electrons adapt themselves instantly to the positions of the much heavier atomic nuclei as the molecule changes shape (the “Born-Oppenheimer approximation”), but this is only approximately true. The electrons, which exhibit both wave and particle aspects, can interfere with each other. The resulting electron wavepackets can oscillate rapidly compared to the motion of the atomic nuclei. Such “electron coherences” are thought to be important in chemical and biological processes such as vision but have been difficult to study due to the extremely short timescales on which they evolve (a few attoseconds, where one attosecond = 0.000000000000000001 seconds). This extremely fast electron motion will be affected by the comparatively slower motion of the atomic nuclei. The PI and her research team will use state-of-the-art lasers and photon sources on the campus of the University of Central Florida to study the evolution of these electron coherences and their coupling to the underlying nuclear motions. Ultimately such studies may advance our ability to engineer reaction products and optimize energy harvesting. This CAREER award supports undergraduate and graduate students and postdoctoral researchers who will be trained in the use of state-of-the-art laser systems and associated advanced spectroscopic techniques. In addition, the award supports an educational and outreach project which includes a summer program focusing on instrumentation training for students, an introductory video sequence on ultrafast science addressing a broader audience, and events for high-school teachers and students, called “Go Ultrafast!”Technical audience abstract: When coherent light interacts with a molecule, multiple electronic states can be populated with specific relative phases, resulting in electronic coherences. In this project, the evolution of these electronic coherences will be time-resolved in a pump-probe scheme with temporal resolutions at the natural time scales of the electron and ion motion. The effect of electron-nuclear coupling on the electronic-coherence properties, such as their lengths, strengths, and revivals, will be investigated. Femtosecond infrared/near-infrared lasers and attosecond XUV/x-ray table-top light sources will be used as the pump or the probe. Electronic coherences will be monitored through electron kinetic energy and abundance variations as a function of the pump-probe delay, using electron-ion spectroscopy of 3-dimensional momentum imaging and transient absorption spectroscopy. Simultaneous measurement of electrons and ions in the momentum space will be used to show the correlation between the evolution of electron dynamics and ion motion. This project will advance our understanding of charge dynamics and photoenergy transformation and transfer mechanisms in molecules and pave a path to photocontrol schemes for directing energy flows. The results will provide reliable references for validation of theoretical methods in the non-Born-Oppenheimer regime.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.