Playing squash with molecules - energy transfer of polyatomic molecules at the gas surface interface

在气体-表面界面处的能量传递过程对于各种物理和化学感兴趣的现象是重要的。它们在多相催化、光开关、染料敏化太阳能电池和大气化学中发挥着至关重要的作用，仅举几例。特别是对于双原子分子，已经非常详细地研究了表面能量转移的基本机制。这包括，除其他外，通过捕获（长寿命复合物），电子非绝热（即振动到电子）耦合，直接机械耦合和电子转移的激发和去激发分子。相比之下，几乎没有实验数据可用于多原子分子在表面碰撞中的能量耗散，这意味着表面过程的理论模型的发展依赖于非常有限的小分子选择。在这个项目中，我计划采用分子束表面散射实验，系统地研究多原子分子的振动和平移激发对表面能量转移过程的影响。实验参数将系统地改变不同的分子和表面以下自下而上的方法。散射分子将通过动力学控制选择性电离（KCSI）来检测，这是一种研究振动激发多原子分子光谱的强大方法，已开发用于纯气相实验。这种方法有利于多原子分子的光谱学，并将首次应用于表面散射实验，提供有关散射分子的振动和平移能量的信息。我将能够解决的问题是根据相关的主题在表面散射的双原子分子：非绝热效应发挥作用的多原子分子和表面之间的相互作用？是一个短暂的阴离子状态的形成有关的振动弛豫的去激发机制？低频模式对振动弛豫机制有什么影响？高振动激发态大分子在低功函数金属散射时振动弛豫是否伴随着电子发射？在探索这些主题时，实验将产生大量的数据，这些数据将作为描述表面动力学的更一般理论模型的开发和改进的基础。

Energy transfer processes at the gas-surface interface are important for a variety of phenomena of physical and chemical interest. They play crucial roles in heterogeneous catalysis, photoswitches, dye-sensitized solar cells and atmospheric chemistry, just to name a few. In particular for diatomic molecules, underlying mechanisms for energy transfer at surfaces have been studied in great detail. This includes, among others, excitation and de-excitation of excited molecules via trapping (long-lived complexes), electronically non-adiabatic (i.e. vibrational to electronical) coupling, direct mechanical coupling and electron transfer. In contrast, almost no experimental data is available for energy dissipation of polyatomic molecules in surface collisions, meaning that the development of theoretical models of surface processes relies on a very limited selection of small molecules. In the proposed project, I plan to methodically study the effect of polyatomic molecules' vibrational and translational excitation on energy transfer processes at surfaces employing molecular beam surface scattering experiments. Experimental parameters will be systematically varied for different molecules and surfaces following a bottom-up approach. Scattered molecules will be detected by Kinetically Controlled Selective Ionization (KCSI), a powerful method to study vibrationally excited polyatomic molecules' spectroscopy that has been developed for pure gas phase experiments. This method facilitates the spectroscopy of polyatomic molecules and will be applied to surface scattering experiments for the first time, providing information about vibrational and translational energy of scattered molecules. I will be able to address questions which are in accordance with topics relevant in surface scattering of diatomic molecules: do non-adiabatic effects play a role in the interaction between polyatomic molecules and surfaces? Is the formation of a transient anionic state relevant for the de-excitation mechanism for vibrational relaxation? What is the influence of low-frequency modes on the vibrational relaxation mechanism? Is vibrational relaxation of highly vibrationally excited large molecules accompanied by electron emission when scattering from low work function metals? In exploring these topics, the experiments will produce a vast amount of data which will serve as basis for the development and refinement of more general theoretical models describing surface dynamics.