CAREER: From Quantum to Classical and Back: Bringing 2D Spectroscopy Insights into Focus

普渡大学的Mike Reppert获得了化学系化学理论、模型和计算方法项目的奖励，以探索二维光谱学中量子和经典相干性之间的相互作用。二维红外光谱（2DIR）和二维电子光谱（2DES）使用超快激光脉冲来监测原子和电子在时间尺度上的运动，其速度超过万亿分之一秒。这样的实验有可能为蛋白质折叠和光合作用等基本生物过程提供前所未有的见解。然而，它们产生的数据通常难以解释，限制了它们在实际应用中的用处。Reppert博士和他的研究小组正在开发新的理论工具，以更好地理解2DIR和2DES信号的物理起源（特别是量子效应和经典效应所扮演的独特角色），为更透明和有效地解释二维数据铺平道路。新开发的2DIR模拟方法将被纳入蛋白质2DIR模拟的在线应用程序，供其他研究人员使用。此外，Reppert小组将与K-12教育工作者合作开发2D声学实验，展示使用声音信号的2DES和2DIR测量的工作原理。总之，这些努力扩大了这些光谱工具的可及性，并扩大了这些二维方法在化学科学中广泛问题的应用。尽管有一系列令人印象深刻的量子和半经典动力学方法可用于模拟二维（2D）光谱，但二维理论库中仍然存在令人惊讶的差距：二维光谱的经典理论或分类量子效应的系统框架尚未得到彻底发展。一方面，这种限制使得完全经典模拟的潜在数值优势在很大程度上没有得到探索；另一方面，由于无法系统地对量子效应和经典效应进行分类，使得耦合分子系统中相干性的物理起源变得模糊。为了探索这些问题，Reppert小组正在努力开发一个系统的、图解的框架，以解开量子和经典对相干振动动力学的贡献，从相对简单的二维红外（2DIR）光谱开始，朝着更复杂的振动动力学和酰胺I（蛋白质C=O拉伸）2DIR实验的定量解释。为了测试相干非线性过程的经典模型的局限性，将设计并实验实施一类新的二维测量来研究声学非线性响应。通过开发教育材料（从K-12到研究生水平），通过概念上可接近的“球和弹簧”模型来说明非线性过程，这项工作的更广泛影响将得到最大化。此外，Reppert小组将把新开发的酰胺I模拟方法整合到AmideSpec应用程序中，为全球研究人员提供一个研究级的在线工具，用于解释蛋白质2DIR数据。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。

Mike Reppert of Purdue University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to explore the interplay between quantum and classical coherence in two-dimensional (2D) spectroscopy. Two-dimensional infrared (2DIR) spectroscopy and two-dimensional electronic spectroscopy (2DES) use ultrafast laser pulses to monitor the motion of atoms and electrons on timescales faster than one trillionth of a second. Such experiments have the potential to provide unprecedented insight into fundamental biological processes such as protein folding and photosynthesis. However, the data they produce is often difficult to interpret, limiting their usefulness in real-world applications. Dr. Reppert and his research group are developing new theoretical tools to better understand the physical origins of 2DIR and 2DES signals (especially the distinct roles played by quantum and classical effects), paving the way for more transparent and efficient interpretation of 2D data. Newly developed 2DIR simulation methods will be made available to other researchers by incorporating them into an online application for protein 2DIR simulations. In addition, the Reppert group will work with K-12 educators to develop 2D acoustic experiments that demonstrate the working principles of 2DES and 2DIR measurements using audible signals. Together, these efforts are expand expand both accessibility to these spectroscopic tools and the application of these 2D methods to a broad class of problems in the chemical sciences. Despite the impressive array of quantum and semiclassical dynamics methods available for simulating two-dimensional (2D) optical spectra, a surprising gap remains in the 2D theory arsenal: no classical theory for 2D spectroscopy or systematic framework for classifying quantum effects has been thoroughly developed. On the one hand, this limitation leaves largely unexplored the potential numerical advantages of fully classical simulations; on the other hand, the inability to systematically classify quantum and classical effects obscures the physical origins of coherence in coupled molecular systems. To explore these issues, the Reppert group is working to develop a systematic, diagrammatic framework for disentangling quantum and classical contributions to coherent vibrational dynamics, beginning with the relatively simple case of 2D infrared (2DIR) spectroscopy and working toward more complex vibronic dynamics and the quantitative interpretation of Amide I (protein C=O stretch) 2DIR experiments. To test the limits of classical models for coherent nonlinear processes, a new class of 2D measurements investigating acoustic nonlinear response will be designed and implemented experimentally. The broader impact of this work will be maximized by developing educational materials (K-12 through graduate level) that illustrate nonlinear processes through conceptually approachable “ball and spring” models. In addition, the Reppert group will incorporate newly developed Amide I simulation methods into the AmideSpec app, offering a research-grade online tool for interpreting protein 2DIR data to researchers around the globe.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.