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

气表面界面上的能量传递过程对各种物理和化学现象都很重要。它们在多相催化、光开关、染料敏化太阳能电池和大气化学等领域发挥着至关重要的作用。特别是对于双原子分子，在表面能量转移的潜在机制已经被非常详细的研究。这包括，除其他外，激发态分子通过捕获（长寿命络合物）的激发和去激发，电子非绝热（即振动到电子）耦合，直接机械耦合和电子转移。相比之下，几乎没有多原子分子在表面碰撞中能量耗散的实验数据，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。在本课题中，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动动激发对表面能量传递过程的影响。实验参数将按照自下而上的方法系统地改变不同的分子和表面。散射分子将通过动力学控制选择电离（KCSI）检测，这是一种研究振动激发多原子分子光谱的强大方法，是为纯气相实验开发的。该方法有利于多原子分子的光谱分析，将首次应用于表面散射实验，提供散射分子的振动和平移能信息。我将能够解决与双原子分子表面散射相关的问题：非绝热效应在多原子分子和表面之间的相互作用中起作用吗？瞬态阴离子态的形成是否与振动弛豫的去激发机制有关？低频模态对振动弛豫机制的影响是什么？当从低功功能金属散射时，高振动激发的大分子的振动弛豫是否伴随着电子发射？在探索这些主题的过程中，实验将产生大量的数据，这些数据将作为发展和完善描述表面动力学的更一般理论模型的基础。

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.