Evaluation of a new VUV-FEL surface science end station using atomic beam surface scattering and velocity-resolved surface reaction dynamics

by Zibo Zhao
Doctoral thesis
Date of Examination:2024-08-27
Date of issue:2024-12-03
Advisor:Prof. Dr. Alec M. Wodtke
Referee:Prof. Dr. Alec M. Wodtke
Referee:Prof. Dr. Dirk Schwarzer
Referee:Prof. Dr. Jürgen Troe
Referee:Prof. Dr. Michael Buback
Referee:Prof. Dr. Daniel Obenchain
Referee:Prof. Dr. Martin Wenderoth
Persistent Address: http://dx.doi.org/10.53846/goediss-10898

 

 

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Abstract

English

Abstract: 1. Atomic oxygen scattering from HOPG It has been unequivocally established that the electronic spin of a molecule significantly influences reactivity in gas phase reactions. However, the presence of clear evidence for spin selection rules in surface chemistry, despite being of widespread interest, remains challenging. Definitive state-to-state experiments demonstrating spin conservation in surface chemical reactions are lacking. In the first study presented in this thesis, we utilized a novel incoming/outgoing correlation ion-imaging technique to conduct atomic scattering experiments involving O(3P) and O(1D) atoms colliding with a highly oriented pyrolytic graphite (HOPG) surface. Notably, the initial spin state distribution was controlled, and the final spin-state distributions were determined. Through this experimental technique, we achieved high-resolution scattering with "spin-state enriched beams with broad velocity distributions." We distinctly observed electronically nonadiabatic pathways in which O(1D) is quenched to O(3P) and releases excess translational energy as O(3P) departs from the graphite surface. Furthermore, we observed a higher sticking probability of O(1D) relative to O(3P) on graphite. Molecular dynamics simulations confirmed spin-selective collisions and revealed the mechanism of spin flipping. 2. N2O decomposition on Pd(110) Another essential aspect of studying the dynamics of surface reactions is to understand the energy transfer processes associated with chemical bond breaking and successive bond formation. Despite the wealth of dynamical information obtained from measuring the internal states of desorption products in surface reactions, the mechanism underlying energy partitioning in these reactions remains largely unclear. In the second system investigated in this thesis, we utilized an ion imaging technique to investigate the quantum-state resolved dynamics of N2O decomposition on Pd(110). Our findings indicate that N2 desorbs directly with an anisotropic sharp angular distribution from the decomposition of N2O adsorbed on bridge sites oriented along the [001] azimuth of the surface. N2 exhibits high rotational excitation up to 𝐽=50 (𝑣′′=0) with a substantial average translational energy of 0.77 eV. By employing classical trajectory simulations based on a high-dimensional, modified potential energy surface (PES) constructed using the EANN approach, we estimated that approximately 60% of the energy released (1.5 eV) from the transition state is transferred to the rotational and kinetic energies of the desorbing N2. The high rotational energy because the nascent N2 molecule experiences a strong torque as it passes through the transition state. The resulting rotational motion is decoupled from the translational energy.
Keywords: Dynamics at Surfaces; Oxygen atom scattering; Velocity-resolved surface reaction dynamics; Ion imaging technique; Free electron laser; Nitrous oxide decomposition; Energy transfer
 
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