Dresden 2017 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 6: Ultrafast Phenoma I

HL 6.7: Talk

Monday, March 20, 2017, 11:45–12:00, POT 51

Ultrafast electron transfer-induced CO₂ activation at a ZnO surface — •Lukas Gierster, Sesha Vempati, and Julia Stähler — Department of Physical Chemistry, Fritz-Haber-Institute of the Max-Planck-Society, Faradayweg 4-6, 14195 Berlin, Germany

Since many years, ZnO has been used as a catalyst which facilitates the conversion of carbon dioxide into valuable chemicals such as methanol [1]. CO₂, which is the most stable carbon oxide species, needs to be activated in order to start hydrogenation. Recent experimental and theoretical work showed that CO₂ adsorbs in a bent configuration with tridentate chemical binding on the ZnO (10-10) surface [1]. However, the energies of the frontier molecular orbitals of the adsorbed CO₂ molecules in the chemical reaction are still not known. We investigate this question using two-photon photoelectron spectroscopy (2PPE), which gives access to occupied and unoccupied electronic states and the dynamics therein. Static photoelectron spectroscopy shows that the work function of the surface increases considerably upon CO₂ adsorption possibly due to a (partial) reduction of the molecules and their dipole moment. A time-resolved pump-probe experiment suggests that electrons are injected from the ZnO substrate into the CO₂ molecules after above band gap photoexcitation of the substrate. The injected electrons populate the CO₂ LUMO, which subsequently shifts down in energy. This leads to a built up of an electronic state just below the Fermi energy within few picoseconds, which is likely to be related to the activated CO₂ molecules.

[1] K. Kotsis, et al., Z. Phys. Chem. 222, 891-915 (2008).