Fundamental mechanisms for molecular energy conversion and chemical reactions at surfaces

Abstract

The dream of theoretical surface chemistry is to predict the outcome of reactions in order to find the ideal catalyst for a certain application. Having a working ab initio theory in hand would not only enable these predictions but also provide insights into the mechanisms of surface reactions. The development of theoretical models can be assisted by experimental studies providing benchmark data. Though for some reactions a quantitative agreement between experimental observations and theoretical calculations has been achieved, theoretical surface chemistry is in general still far away from gaining predictive power. Here we review recent experimental developments towards the understanding of surface reactions. It is demonstrated how quantum-state resolved scattering experiments on reactive and nonreactive systems can be used to test front-running theoretical approaches. Two challenges for describing dynamics at surfaces are addressed: nonadiabaticity in diatomic molecule surface scattering and the increasing system size when observing and describing the dynamics of polyatomic molecules at surfaces. Finally recent experimental studies on reactive systems are presented. It is shown how elementary steps in a complex surface reaction can be revealed experimentally.

Atom-surface van der Waals potentials of topological insulators and semimetals from scattering measurements

“…Since the earliest scattering experiments of atomic beams from surfaces, the phenomenology of resonant scattering and its connection to molecular adsorption at a surface has been known 1,2 . Understanding the scattering of atoms and molecules from surfaces forms a central point of many aspects in physical chemistry, including chemical reaction at surfaces and providing the link for an atomistic understanding of heterogeneous catalysis [3][4][5] . Scattering experiments provide access to the atom-surface interaction potential which is the necessary prerequisite for any quantitative description and theoretical treatment of molecular adsorption 6 or surface reaction processes.…”

“…Scattering experiments provide access to the atom-surface interaction potential which is the necessary prerequisite for any quantitative description and theoretical treatment of molecular adsorption 6 or surface reaction processes. Scattering approaches to chemisorption 7,8 and the coordinates relevant to the reaction potential [3][4][5] rely on such treatment.…”

Transfer-matrix theory of surface spin-echo experiments with molecules

“…A proper analysis of the resulting experimental signal must be based on (i) the solutions of the time-dependent Schrödinger equation accounting for the development of entanglement between the translational motion and the internal states of molecules in the beam, as the beam transverses the magnetic fields of the spin-echo apparatus; (ii) the description of the molecule-surface scattering events in the relevant frame of reference by the scattering matrix involving all relevant molecular states. This is a challenging task because the potential energy surfaces for molecule-surface interactions are difficult to compute with sufficient accuracy [54][55][56][57][58][59][60], the calculations of the cross sections for molecule-surface scattering are extremely time consuming [61,62] and because the orientation and strength of magnetic fields necessarily change throughout the spin-echo apparatus. An alternative formulation can be developed to treat the molecule-surface scattering matrix elements as varying parameters to be determined from the experimental interferometry signal by one of the algorithms used in optimal control theory [63][64][65][66][67][68] or reinforcement machine learning designed to solve the inverse problem [69,70].…”

Time-of-flight measurements of the low-energy scattering of CH4 from Ir(111)

“…[5][6][7] Developing an ab initio theory capable of predicting gas-surface interaction outcomes, which is necessary for finding suitable catalysts for technological applications as well as for providing insights into the mechanisms of surface reactions, requires experimental studies to assess its predictive power. 8 Experimental studies of methane scattering from metal surfaces are technically challenging as the scattered intensities are usually low, comparable to background intensities from the residual gas in a UHV chamber, and methane does not have any suitable schemes for detection by Resonance-enhanced multiphoton ionization. 8 The present study is the continuation of a line of work aimed at undestanding the low-energy scattering dynamics of CH 4 from metal surfaces.…”