Gas-phase ion reaction dynamics

内能在决定化学反应动力学的结果方面起着重要的作用。 在过去的七年里，我的小组一直在研究气相离子的单分子反应的机制和竞争动力学，特别是静电结合的复合物。 由于对亚稳态络合物进行的质谱实验的性质，单分子反应的内能和动力学被很好地定义。 然而，当进行基于碰撞的实验时，这一点就被打破了。 在这些试图在高层大气中复制粒子轰击的研究中，所产生的激发离子的内能是不明确的。 因此，我们的研究扩展到学习内部能量沉积在气相离子在高（keV）和低（eV）能量碰撞事件，通过检查他们的解离特性和光谱。 最近完成的设备允许我们探索从气相离子和中性目标气体之间的碰撞荧光从190 nm - 1000 nm在我们的质谱仪作为碰撞能量（实验室框架）从8 keV到100 eV的函数（请记住，在这些能量下沉积到物质中的内部能量远远小于碰撞能量）。 通过阈值光电子-光离子符合光谱（TPEPICO）对离子从阈值到> 30 eV的解离进行的平行研究使我们能够将质谱和荧光观察结果与碎片离子出现的可靠能量阈值进行比较-从而允许在基于碰撞的实验中定量内部能量沉积。

Internal energy plays an important role in determining the outcome of the dynamics of chemical reactions.  Over the last seven years my group has been involved in studying the mechanisms and competing kinetics of unimolecular reactions of gas-phase ions - notably electrostatically bound complexes.  Due to the nature of the mass spectrometric experiments performed on metastable complexes the internal energy, and hence kinetics, of the unimolecular reactions are quite well defined.  This breaks down, however, when collision-based experiments are performed.  In these studies, which attempt to replicate particle bombardment in the upper atmosphere, the internal energy of the resulting excited ion is ill-defined.  Our research has thus expanded into learning about internal energy deposition in gas-phase ions in both high (keV) and low (eV) energy collision events by examining their dissociation characteristics and their spectroscopy.  A recently completed apparatus allows us to explore the fluorescence from collisions between gas-phase ions and neutral target gases from 190 nm - 1000 nm in our mass spectrometer as a function of collision energy (laboratory frame) from 8 keV to 100 eV (keeping in mind that the internal energy deposited into the species at these energies is considerably less than the collision energy).  Parallel investigations into the dissociation of ions from threshold to > 30 eV by threshold photoelectron-photoion coincidence spectroscopy (TPEPICO) allow us to compare our mass spectrometric and fluorescence observations with reliable energy thresholds for the appearance of fragment ions - thus permitting the quantitation of internal energy deposition in collision-based experiments.