Femtosecond Nonlinear Spectroscopic Studies of Chemical Reactions in Condensed Phases

在化学部实验物理化学计划的支持下，乔纳斯将研究溶液中化学反应的基本步骤。为了解决液体中分子无特征光谱下的动力学问题，将发展两种新型的多脉冲飞秒非线性光谱学。一种技术将使用三脉冲序列来准备和研究热激活化学反应的过渡态，时间分辨率约为20飞秒。第二种方法是利用光谱干涉法从四波混频信号中获得完整的电场信息，如利用外差探测光子回波。实验将研究溶剂在烷基碘单分子离子解离中的作用，目的是确定单分子离子解离是由溶剂波动还是分子内振动激发激活的。溶剂对化学反应的速度有很大影响。它们通过改变溶质分子的内部能量结构、改变反应机理或允许新的反应路径来做到这一点。在这个项目中，两项新的实验技术将被用于实验，旨在探索溶剂对几种不同类型的反应的影响，例如那些通过提高温度而加速的反应。这些研究的结果应该有助于我们理解溶剂效应在这些不同反应中的重要性。这样的知识有助于确定溶液中的反应应该在什么条件下进行以获得最佳的预期结果。

In this project supported by the Experimental Physical Chemistry Program of the Chemistry Division, Jonas will study the elementary steps of chemical reactions in solution. Two new types of multiple-pulse femtosecond nonlinear spectroscopy will be developed in order to resolve the dynamics beneath the featureless spectra of molecules in liquids. One technique will use a three-pulse sequence to prepare and study transition states for thermally activated chemical reactions with a time resolution on the order of 20 femtoseconds. The second method will obtain the complete electric field information from four-wave mixing signals such as the photon echo by heterodyne detection using spectral interferometry. Experiments will study the role of the solvent in the unimolecular ionic dissociation of alkyl iodides with the aim of determining whether unimolecular ionic dissociation is activated by solvent fluctuations or intramolecular vibrational excitation. Solvents have dramatic effects on the rates of chemical reactions. They do this by altering the internal energy structure of solute molecules, changing the reaction mechanisms, or allowing new reaction paths. In this project two new experimental techniques will be used in experiments which are designed to probe the effect of solvents on a few different types of reactions, such as those which are expedited by increasing temperature. The results of these studies should help us understand how important solvent effects are in these different reactions. Such knowledge can help determine the conditions under which reactions in solution should be run for optimal desired results.