Lecture
Van Marum Colloquium: Hydrogen interactions with metal surfaces: nuclear spin conversion and adsorption
- Date
- Monday 24 June 2024
- Time
- Location
-
Gorlaeus Building
Einsteinweg 55
2333 CC Leiden - Room
- CE.0.18
Abstract
Hydrogen interacting with surfaces has attracted much attention, because of its relevance to many chemical processes. Therefore, understanding of their interactions is of great interest not only from a fundamental point of view but also in industrial applications. In my presentation, hydrogen in molecular and atomic adsorption on metal surfaces are focused.
\Two nuclear-spin modifications exist for H2, i.e., ortho-H2 (o-H2) and para-H2 (p-H2). Due to quantum-mechanical symmetry restrictions, the rotational (quantum number J) states of molecular hydrogen couple with its nuclear-spin states. While for an isolated H2 interconversion between these two species, ortho-para (o-p) conversion is forbidden, it is known that the conversion is promoted on various solid surfaces [1]. The o-p conversion is accompanied by the rotational-state transition as well as the nuclear-spin flip. As the 1st topic of my presentation, I will talk about o-p conversion of molecularly chemisorbed H2 on Pd(210). Studying the o-p conversion of H2 on surface allows us to understand the rotational-energy transfer process which is not well-understood compared with other degrees of freedom the molecules possess such as translation and vibration. It is found that rotational-energy is transferred to surface phonons as well as surface electrons in o-p conversion [2].
Internal degrees of freedom in molecules such as vibration and rotation, play an important role in chemical reactions at surfaces. As another internal degree of freedom, the electronic spin effects in surface reactions are dealt in the 2nd topic of my presentation. Atomic hydrogen (H) consists of an electron and a proton, each having spin 1/2. While the adsorption of H on surfaces is regarded as a proto-type reaction in surface chemistry, which has been extensively studied on various surfaces to date [3], the role of the spin degree of freedom of H still remains unclear. Using a spin polarized atomic hydrogen beam [4], the spin effects in H adsorption and abstraction reactions on Ni(111) are studied. The results indicate that, the H reactivity is higher when its spin is oriented parallel to the surface spin direction of the Ni(111) compared with its spin direction is perpendicular to the surface [5].
References
- K. Fukutani and T. Sugimoto, Prog. Surf. Sci., 88, 279 (2013).
- H. Ueta and K. Fukutani, J. Phys. Chem. Lett., 14, 7591 (2023).
- M. S. Hofman, D. Z. Wang, Y. Yang and B. E. Koel, Surf. Sci. Rep. 73, 153 (2018).
- Y. Nagaya, H. Nakatsu, S. Ogura, K. Shimazaki, H. Ueta, K. Takeyasu and K. Fukutani, J. Chem. Phys., 155, 194201 (2021).
- H. Ueta, Y. Ohashi, Z-D. Sun, T. Ozawa and K. Fukutani, in preparation.