Anharmonicities and Nonlinearities in the Ultrafast Dynamics of Liquids

布朗大学的Richard Stratt得到理论和计算化学项目的支持，开发采用瞬时简正模（INM）方法来探索液体中多原子分子内的分子内振动能流的方法，以及通过五阶二维拉曼光谱揭示的分子间液体动力学。 最近的进展，将动力学非谐性和非线性相互作用的INM形式主义，预计将有助于揭示分子之间的竞争途径选择分子内振动能量弛豫的方式，并帮助确定的量的退相预期从不同的分子间运动。 我们也希望能深入了解在各种光谱环境中导致均匀展宽的事件。液体中的化学过程发生在非常广泛的时间尺度上，但许多关键的"触发"事件似乎发生在万亿分之一秒以下的时间。 当人们在分子水平上考察能量如何在液体中流动时，这种二分法尤其明显。 将分子振动中的能量释放到周围的溶液中可能需要万亿分之一秒到几秒的时间，但这种过程是由溶剂摩擦驱动的，其寿命总是小于万亿分之一秒。 直到最近，实验技术才能够在这些超快的时间尺度上检查液体中的振动，并具有足够的复杂性来了解液体动力学中的潜在分子机制。 该项目旨在开发一个框架来解释这些具有挑战性的新实验的结果，这些实验研究溶解在液体中的分子的振动能量弛豫途径。

Richard Stratt of Brown University is supported by the Theoretical and Computational Chemistry Program to develop methods employing the instantaneous normal mode (INM) approach to explore intramolecular vibrational energy flow within polyatomic molecules in liquids, and the intermolecular liquid dynamics revealed by fifth order two-dimensional Raman spectroscopy. Recent progress in incorporating dynamical anharmonicities and nonlinear interactions into the INM formalism are expected to help reveal the ways in which molecules choose between competing pathways for intramolecular vibrational energy relaxation, and help to identify the amount of dephasing to be expected from different intermolecular motions. Insights are also expected into the events that lead to homogeneous broadening in a variety of spectroscopic venues.Chemical processes in liquids take place over a tremendously wide range of time scales, but many of the key "triggering" events seem to occur in times well under a trillionth of a second. This dichotomy is especially evident when one examines how energy flows in liquids at a molecular level. It can take anywhere from a trillionth of a second to seconds to release the energy buried within the vibrations of a molecule into the surrounding solution, but such processes are driven by a solvent friction whose lifetime is invariably less than a trillionth of a second. Only relatively recently, experimental techniques have been able to examine vibrations in liquids at these ultrafast time scales and with sufficient sophistication to learn about underlying molecular mechanisms in the dynamics of liquids. This project aims to develop a framework to interpret the results from these challenging new experiments that study vibrational energy relaxation pathways in molecules dissolved in liquids.