On May 22, 2023, the experimental team of Professor Alec M. Wodtke of the Max Planck Institute for Multidisciplinary Science, Germany and the theoretical team of Professor Guo Hua of the University of New Mexico published a report entitled “Spin-dependent reactivity and spin-flipping dynamics in oxygen atom scattering from” in the journal Nature Chemistry Graphite”.
In this study, the scattering experimental results of three-wire oxygen atom O(3P) and singlet oxygen atom O(1D) on the surface of highly directional pyrolytic graphite (HOPG) are reported, and the spin-selective collision of oxygen atoms on the graphite surface is confirmed by molecular dynamics simulation, and the mechanism of spin flipping is revealed.
The corresponding author of the paper is G. Professor Barratt Park and Professor Guo Hua, co-first authors are Zibo Zhao and Yingqi Wang.
For gas-phase reactions, it is well established that changing the electron spin state of a molecule can greatly change its reactivity. However, there is a lack of clear experiments that can observe state-to-state conserved spin reactions. Therefore, the role of electron spin in surface chemistry remains quite controversial.
Professor Alec M. Wodtke’s experimental team at the Max Planck Institute for Multidisciplinary Science, Germany, used a novel Incoming/Outgoing Correlation Ion-imaging method to measure the kinetic energy and angular distribution of state-to-state scattered oxygen atoms. This method greatly improves the velocity resolution, allowing the probability of reaction at a given incident energy to be measured, even with a wide velocity distribution of incident and scattered atoms. Through this method, the electron non-adiabatic path of O(1D) scattering on the graphite surface is found, that is, the incident O(1D) leaves the surface with O(3P) after scattering on the graphite surface, and in this process, part of the electron energy of the O(1D) excited state is converted into O(3P) scattering kinetic energy and the remaining part is absorbed by the surface. In addition, the experimental team also observed that O(1D) has a higher adsorption probability on graphite than O(3P).
In order to understand the dynamic process of O(3P) and O(1D) scattering on the graphite surface, the theoretical team of Professor Guo Hua of the University of New Mexico used machine learning methods to establish high-dimensional potential energy surfaces (PESs) of oxygen atoms on the graphene surface from DFT data, and carried out spin-selective molecular dynamics simulations. The simulation results show that O(1D) reacts with graphite more efficiently than O(3P), showing a higher adsorption probability. The incident O(3P) always maintains its spin during graphite collisions. In contrast, the spin flip after the O(1D) atom collides with graphite requires the formation of chemically adsorbed oxygen atoms excited by high vibration on the surface, thereby losing most of the kinetic energy. Theoretical simulations qualitatively explain the experimental results.
Figure 1: O(3P)→Kinetic energy and angular distribution in O(3P) processes and comparison with non-adiabatic and adiabatic molecular dynamics simulations.
The study shows that for surface reactions, changes in the spin state of molecules may still have a large impact on reaction activity, in which non-adiabatic effects play an important role. This has important implications for future surface reaction studies: the spin state of molecules is an important factor in determining reaction activity, while the spin flipping of molecules does not follow the conventional adiabatic path. (Source: Science Network)
Related paper information:https://doi.org/10.1038/s41557-023-01204-2
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