Anharmonicities and Nonlinearities in the Ultrafast Dynamics of Liquids

布朗大学的理查德·m·斯特拉特（Richard M. Stratt）得到了化学系理论与计算化学项目的奖励，继续他的研究，研究哪些特定的集体或个人运动以及哪些分子参与了液体和溶剂中能量转移的基本步骤。大多数液体实验研究分析的基础是线性响应的假设：在实验过程中施加的外部扰动的任何细节都不会对答案产生太大的影响。这项研究表明，它们提供了学习非线性行为的机会，而不是将这些例子视为例外。特别是，最近一些涉及液体中高度旋转激发分子的弛豫和溶质电子激发后溶剂非线性光谱演变的实验，提供了非线性响应的有趣案例研究。这些和相关的例子正在进行理论研究，以了解诸如分子尺度摩擦等概念在多大程度上具有自然的非线性推广，并试图了解产生这些非线性的原因以及它们如何在皮秒和亚皮秒时间尺度上表现出来。这项工作通过其对生物学和其他领域重要的基本物理过程的阐明，以及通过PI向普通受众解释这些基本分子过程的努力，产生了更广泛的影响。

Richard M. Stratt of Brown University is supported by an award from the Theoretical and Computational Chemistry program within the Division of Chemistry to continue his research examining which specific collective or individual motions, and which molecules, are participating in the fundamental steps of energy transfer in liquids and in solvation. Underlying the analysis of most experimental studies of liquids is the assumption of linear response: that none of the details of the external perturbations applied in the course of an experiment make much difference in the answer. This research is showing that, rather than viewing such examples as exceptions, they provide opportunities for learning about nonlinear behavior. In particular, some recent experiments involving the relaxation of highly rotationally excited molecules in liquids and the evolution of the nonlinear spectroscopy of a solvent following the electronic excitation of a solute are providing intriguing case studies of nonlinear response. These and related examples are being examined theoretically in order to see to what extent concepts such as molecular-scale friction have natural nonlinear generalizations, and to try to learn both what it is that generates these nonlinearities and how they manifest themselves on picosecond and sub-picosecond time scales. This work is having a broader impact both through its illumination of fundamental physical processes important in biology and elsewhere and through the efforts of the PI to explain these fundamental molecular processes to general audiences.