Picosecond Dynamics of Organic Ionic Intermediates

9408354皮秒吸收光谱学将研究卤代烃和乙烯基卤化物的光解动力学。反应机理包括均解和异解，在极性溶剂中生成自由基对和接触离子对。在皮秒时间尺度上，接触离子对通过共价键的形成和扩散分离而衰变，形成溶剂分离的离子对。后者通过塌缩成接触离子对或扩散分离成自由离子而衰变。该项目将包括：(1)研究自由基对和接触离子对的光化学产生的机理，(2)碳正离子和阴离子之间形成共价键的活化参数的确定，以及溶剂对这一过程的影响，(3)溶剂对接触离子对和溶剂分离离子对之间相互转化的作用，以及这如何取决于离子的分子结构。有机动力学项目的这笔赠款支持科罗拉多大学凯文·S·彼得斯教授的继续工作。皮秒(十亿分之一秒)区域的脉冲紫外线激光将被用来打破碳-氯键，目的是产生带正电的碳物种(碳正离子)。这些活性中间体可能与带负电荷的物种(阴离子)直接接触，或者碳阳离子和阴离子可能被有限数量的溶剂分子分开。这些接触和溶剂分离的离子对作为溶剂和分子结构的函数的动态行为将被研究。

9408354 Peters U. of Colorado The dynamics of photodissociation of alkyl and vinyl halides will be examined by picosecond absorption spectroscopy. The reaction mechanism involves both homolysis and heterolysis to produce radical pairs and contact ion pairs in polar solvents. On the picosecond time-scale the contact ion pairs decay by covalent bond formation as well as diffusional separation to form solvent separated ion pairs. The latter species decay by collapse to a contact ion pair or diffusionally separate to free ions. The project will include: (1) An investigation of the mechanism for the photochemical production of radical pairs and contact ion pairs, (2) The determination of activation parameters for covalent bond formation between a carbocation and an anion, and how solvent effects this process, (3) The role of solvent on the inter conversion between contact and solvent separated ion pairs, and how this depends on molecular structure of the ions. This grant by the Organic Dynamics Program supports the continuing work of Professor Kevin S. Peters at the University of Colorado. A pulsed ultraviolet laser beam in the picosecond (one billionth of a second) domain will be used to break carbon-chloride bonds with the goal of generating positively charged carbon species (carbocations). These reactive intermediates may be in direct contact with a negatively charged species (an anion) or the carbocation and anion may be separated by a limited number of solvent molecules. The dynamic behavior these contact and solvent separated ion pairs as a function of solvent and molecular structure will be investigated.