Kinetics of Gas-Phase Ion Association and Dissociation

在化学系实验物理化学项目中，凯斯西储大学的罗伯特·邓巴将使用离子回旋共振离子陷阱研究气相离子与激光相互作用的性质。“中到大型”碳氢化合物、有机金属化合物、团簇和络合离子是研究的对象。包括时间分辨的光解离动力学、激发离子辐射冷却速率的测量、红外多光子解离动力学、辐射缔合效率的测定以及络合离子解离产物中振动能的分配。其中一些过程的温度依赖性将使用冷却到77K的离子陷阱来确定，理论研究将与一位精通统计力学的专家一起进行，以处理红外多光子解离和辐射缔合。被称为离子回旋共振光谱技术的发展使科学家能够在相对较长的时间内捕获带电的原子或分子，即离子，时间在几秒钟或更长的数量级。有了如此长的存储时间，现在可以更容易地研究涉及持续时间长达数秒的离子的各种过程。这类过程的例子包括离子在吸收光后分裂，光的能量刚好足以切断原子之间的键(接近阈值的光解离)和发射红外辐射。邓巴教授的工作将使他能够研究各种相当大的分子离子的几个“缓慢”的化学过程。

In this project in the Experimental Physical Chemistry Program of the Chemistry Division, Robert Dunbar of Case Western Reserve University will study the properties of gas-phase ions interacting with laser light using an ion cyclotron resonance ion trap. "Medium-to-large" hydrocarbons, organometallic compounds, clusters, and complex ions are targets for study. Time-resolved photodissociation kinetics, measurement of radiative cooling rates of excited ions, infrared multiphoton dissociation kinetics, the determination of radiative association efficiencies and of partitioning of vibrational energy in the products of complex ion dissociation will all be examined. The temperature dependence of some of these processes will be determined using an ion trap cooled to 77 K. Theoretical studies will be conducted dealing with infrared multiphoton dissociation and radiative association in conjunction with an expert versed in statistical mechanics. %%% The development of the technique known as Ion Cyclotron Resonance Spectroscopy has enabled scientists to trap electrically charged atoms or molecules, known as ions, for relatively long times, on the order of seconds or longer. With such long storage times, various processes involving ions which last up to seconds in time can now be studied more easily. Examples of such processes include the breakup of an ion after the absorption of light with just enough energy to sever the bonds between atoms (near-threshold photodissociation) and the emission of infrared radiation. Professor Dunbar's work will allow him to study several of these "slow" chemical processes for a variety of fairly large molecular ions.