Zernike Institute for Advanced Materials Colloquium Thorsten Klüner
|04 October 2012||FWN-Building 5111.0080, Nijenborgh 4, 9747 AG, Groningen|
|Speaker:||Prof. Dr. Thorsten Klüner|
Carl von Ossietzky Universität Oldenburg, Institut für Reine und Angewandte ChemieTheoretische Chemie, Carl-von-Ossietzky Str.9-11, 26129 Oldenburg, Germany
|Title:||Ab initio surface photochemistry|
|Date:||Thu Oct 4, 2012|
|Start:||16.00 (Doors open and coffee available at 15.30)|
Photodesorption of small molecules from surfaces is one of the most fundamental processes in surface photochemistry. Despite its apparent simplicity, a microscopic understanding beyond a qualitative picture still poses a true challenge for theory. While the dynamics of nuclear motion can be treated on various levels of sophistication, all approaches suffer from the lack of sufficiently accurate potential energy surfaces, in particular for electronically excited states involved in the desorption scenario.
In the last decade, we have developed a systematic and accurate methodology to reliably calculate accurate ground and excited state potential energy surfaces (PES) for different adsorbate-substrate systems. These potential energy surfaces serve as a prerequisite for subsequent quantum dynamical wave packet calculations, which allow for a direct simulation of experimentally observable quantities such as velocity distributions. In this talk, I will focus on recent results obtained for photodesorption of NO and CO from a NiO(100) surface. In contrast to previous studies, we were able to construct highly accurate potential energy surfaces based on correlated quantum chemical calculations (CASPT-2/CCSD(T)). Despite the enormous computational cost, this level of theory turns out to be crucial, since less sophisticated approaches such as density functional theory (DFT) cannot even provide a reliable description of ground state properties, not to mention electronically excited states.
These potential energy surfaces were used in subsequent wave packet studies which reveal new desorption mechanisms. In the NO/NiO(100) case, we observed an anti-Antoniewicz scenario in which the wave packet is initially repelled from the surface but eventually reaches a turning point before it is back-scattered from the surface. State resolved desorption velocity distribution have been calculated, and the results are in good agreement with experimental findings. In the CO/NiO(100) system, we observe the formation of a genuine covalent bond upon photoexcitation for the first time. As demonstrated in the current study, this chemical bond formation is the crucial step in the desorption mechanism for this system. Again, our results are in good agreement with recent experiments.
|Last modified:||22 October 2012 2.30 p.m.|