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

• Applicant: Privatdozent Dr. Tim Schäfer
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 311018441

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.

• DFG Programme: Research Grants