Spectroscopy and Reaction Dynamics of Activated Entrance Channel Complexes

宾夕法尼亚大学的玛莎·莱斯特正在进行的研究中，她得到了实验物理化学计划的支持，以表征由羟基自由基和反应性分子伙伴(一氧化碳、一氧化氮、水)组成的振动激活的入口通道络合物的分子间势能、非弹性散射和反应动力学。红外激发将提供足够的能量来克服反应的活化势垒，而分子间激发将使反应物定向，使络合物的结构接近过渡态的结构。莱斯特教授将使用双共振技术记录羟基伸展的中红外光谱和近红外光谱，以及羟基络合物的分子间弯曲能级。光谱测量应该给出基态和振动激发的反应物进入反应通道的势能面的信息。羟基自由基在低层大气的化学中起着关键作用。它被称为“大气的清洁剂”，因为它的反应阻止了大多数微量气体在大气中的积累，其中许多会成为空气污染物和温室气体。对于发射到对流层的大多数含氢分子来说，与OH自由基的反应是它们主要的(如果不是唯一的)化学损失过程。因此，与OH自由基的反应导致这些化合物从大气中移除，并限制了它们在大气中的浓度。许多实验工作已经被用来评估在大气中遇到的条件下的OH自由基动力学和反应机理。在这些研究中，莱斯特教授将使用她实验室开发的技术，更仔细地观察OH自由基与一氧化碳、一氧化氮和水等与大气相关的分子伙伴的反应动力学。

Marsha Lester of the University of Pennsylvania is supported by the Experimental Physical Chemistry Program in her ongoing studies to characterize the intermolecular potential, inelastic scattering and reaction dynamics of vibrationally activated entrance channel complexes composed of a hydroxyl radical and a reactive molecular partner (carbon monoxide, nitric oxide, water). Infrared excitation will provide sufficient energy to overcome the activation barrier to reaction while intermolecular excitations will orient the reactants such that the structure of the complex approximates that of the transition state. Prof. Lester will use double resonance techniques to record the mid- and near-IR spectra of the OH stretch as well as intermolecular bending levels of the OH complexes. Spectral measurements should yield information on the potential energy surfaces in the entrance channel to reaction for ground state and vibrationally excited reactants. The hydroxyl radical plays a pivotal role in the chemistry of the lower atmosphere. It is known as the `atmosphere's detergent` because its reactions prevent the accumulation of most trace gases in the atmosphere, many of which would act as air pollutants and greenhouse gases. For the majority of hydrogen-containing molecules emitted into the troposphere, reaction with the OH radical is their major, if not sole, chemical loss process. Thus, reaction with OH radicals leads to the removal of these compounds from the atmosphere and limits their atmospheric concentrations. Much experimental work has already been performed to evaluate the OH radical kinetics and reaction mechanisms under the conditions encountered in the atmosphere. In these studies, Prof. Lester will use techniques developed in her laboratory to take a much closer look at the reactions dynamics of OH radicals with molecular partners of atmospheric relevance such as carbon monoxide, nitric oxide and water.