Gas-phase ion reaction dynamics

内能在决定化学反应动力学的结果中起着重要的作用。在过去的七年里，我的团队一直参与研究气相离子--特别是静电束缚的络合物--单分子反应的机制和竞争动力学。由于对亚稳态络合物进行的质谱学实验的性质，单分子反应的内能以及动力学都有很好的定义。然而，当进行基于碰撞的实验时，这一点就被打破了。在这些试图复制高层大气中粒子轰击的研究中，由此产生的激发离子的内能定义不明确。因此，我们的研究扩展到通过检查它们的解离特性和光谱来了解高能和低能碰撞事件中气相离子的内能沉积。最近完成的一个装置允许我们在质谱仪中从190 nm-1000 nm探索气相离子与中性目标气体之间碰撞产生的荧光，作为碰撞能量的函数(实验室框架)，从8keV到100 eV(记住，在这些能量下沉积到物种中的内能相当大小于碰撞能量)。对离子从阈值到&gt的解离进行了平行研究；30 eV的阈值光电子-光离子符合谱(TPEPICO)使我们能够将我们的质谱学和荧光观测结果与碎片离子出现的可靠能量阈值进行比较，从而能够在基于碰撞的实验中对内部能量沉积进行量化。

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.