First-principles studies of time-resolved nonlinear optical spectroscopy signals

俄勒冈大学的Jeffrey A.Cina在化学系化学理论、模型和计算方法计划的支持下，开发和实施理论方法，使来自浓缩分子系统的两类时间分辨光谱信号能够进行第一性原理计算和解释。在一个领域，Cina和他的同事们正在努力预测基于共振耦合电子势能面从头计算的超快相位相干多维电子光谱测量的结果。这一方向的进展依赖于一种新理论的形成和实施，该理论基于系统地将所有分子内和分子间的振动自由度划分为与相关电子跃迁强耦合的自由度和弱耦合或非耦合的自由度。理论研究的另一个领域涉及进一步发展和应用量子/半经典混合方法来模拟和解释嵌入在低温晶体中的小分子的时间分辨光谱信号。这些系统的一个基本特征是存在少量相对高频的振动自由度，我们的理论对其动力学进行了严格的数值处理，加上大量服从半经典近似的低频振动，这些系统正在由加州大学欧文分校的V.Ara Apkarian和同事进行实验研究。这项工作通过教育和培训研究生和本科生，与实验研究人员合作构建和解决复杂的理论和计算问题，产生了更广泛的影响。科学影响包括开发适用于分子科学中广泛感兴趣的重大问题的计算工具。我们的理论研究的这两个方面都有可能促进自然和人工光合成能量收集以及基于分子的量子信息处理领域的进步。

Jeffrey A. Cina of the University of Oregon is supported by the Chemical Theory, Models and Computational Methods program in the Chemistry Division to develop and implement theoretical methods enabling the first-principles calculation and interpretation of two classes of time-resolved spectroscopic signals from condensed molecular systems. In one area, Cina and his coworkers are endeavoring to predict the results of ultrafast phase-coherent multidimensional electronic spectroscopy measurements based on the ab initio determination of resonantly coupled electronic potential energy surfaces. Progress in this direction relies on the framing and implementation of a new theory based on systematically partitioning all intra and intermolecular vibrational degrees of freedom into those that are strongly coupled to the relevant electronic transitions and those that are weakly coupled or not coupled. The other area of theoretical study involves the further development and application of a mixed quantum/semiclassical method for the simulation and interpretation of time-resolved spectroscopic signals from small molecules embedded in low-temperature crystals. An essential feature of these systems, which are under experimental study by V. Ara Apkarian and co-workers at UC-Irvine, is the existence of a small number of relatively high-frequency vibrational degrees of freedom, whose dynamics our theory treats numerically rigorously, coupled to a large number of lower-frequency vibrations amenable to semiclassical approximation. This work has a broader impact through the education and training of graduate and undergraduate students to frame and solve complex theoretical and computational problems in collaboration with experimental investigators. Scientific impacts include the development of computational tools applicable to significant problems of widespread interest in molecular science. Both aspects of our theoretical research have the potential to contribute to progress in the areas of natural and artificial photo-synthetic energy harvesting, and molecule-based quantum information processing.