Vibrational Spectroscopy and Reaction Dynamics of Complexes and Reactive Intermediates

宾夕法尼亚大学的玛莎·莱斯特（Marsha Lester）在实验物理化学项目的支持下进行实验，研究基本化学反应的反应途径，包括OH + CO生成HOCO并随后分解为H +二氧化碳的可逆反应，以及OH + HCl生成水+ Cl的反应。从入口通道到过渡态沿反应路径的势能面将通过反应物配合物的分子内和分子间振动模式的红外光谱来绘制。过渡态区也将通过HOCO反应中间体的振动泛音研究来表征，这将获得理论上预测的HOCO预解离共振。配合物和反应中间体将光解生成，它们的振动泛音光谱将使用各种激光泵浦探测方法得到。反应物配合物的结构和稳定性有望揭示它们在反应动力学中的作用，并可能解释这些反应中观察到的异常温度行为。配合物和反应中间体的振动活化将提供足够的能量来诱导非弹性和/或反应性散射动力学，为探索反应势能面提供了一种补充方法。振动激发的配合物和中间体的寿命将由直接的时域测量或谱线在频域的展宽来确定。将研究非弹性散射碎片和反应产物的量子态分布，以及这些衰变过程之间的分支。分子内和/或分子间模式的选择性激发和同位素取代将被用来制备通过化学反应优先衰变的初始态。在过去的十年里，化学反应动力学的实验和理论研究取得了许多进展。这些研究的重点是直接评估远程力对化学反应的影响，探索在大气和燃烧化学中具有实际意义的过程。

Marsha Lester of the University of Pennsylvania is supported by the Experimental Physical Chemistry Program to perform experiments that examine reaction pathways of fundamental chemical reactions, including the reversible reaction of OH + CO to form HOCO with subsequent decomposition to H + carbon dioxide, and the reaction of OH + HCl to form water + Cl. The potential energy surface along the reaction pathway from the entrance channel to the transition state will be mapped via infrared spectroscopy of intra- and inter-molecular vibrational modes of the reactant complexes. The transition state region(s) will also be characterized by vibrational overtone studies of the HOCO reactive intermediate, which will access theoretically predicted predissociative resonances of HOCO. The complexes and reactive intermediates will be generated photolytically, and their vibrational overtone spectra will be obtained using various laser pump-probe methods. The structure and stability of the reactant complexes are expected to reveal their role in the reaction dynamics, and may explain unusual temperature behavior observed for these reactions. Vibrational activation of the complexes and reactive intermediates will supply sufficient energy to induce inelastic and/or reactive scattering dynamics, providing a complementary way to explore the reactive potential energy surfaces. The lifetime of the vibrationally excited complexes and intermediates will be determined by direct time-domain measurements or by spectral line broadening in the frequency domain. Quantum state distributions of inelastically scattered fragments and reaction products will be examined, as well as the branching between these decay processes. Intra-and/or inter-molecular mode selective excitation and isotopic substitution will be utilized to prepare initial states that preferentially decay by chemical reaction. There have been many advances in experimental and theoretical investigations of chemical reaction dynamics over the past decade. These studies focus on directly evaluating the influence of long-range forces on chemical reactions, exploring processes that are of practical importance in atmospheric and combustion chemistry.