Calculation of two-dimensional potential energy surfaces of CO on a rutile(110) surface: ground and excited states

Abstract

Being one of the most important catalytically active metal oxide surfaces, the aim of this study was the description of the laser-induced photodesorption of the CO adsorbate from a TiO₂(110) surface. As a first step, this paper presents two-dimensional potential energy surfaces of a CO molecule on a rutile TiO₂(110) surface. Focussing on the desorption mechanism taking place in this adsorbate–substrate system, the quantum chemical and quantum dynamical calculations regarding the desorption coordinate Z and the polar angle θ allowed a first insight into the mechanistic processes in the CO–TiO₂(110) system which are relevant for laser-induced photodesorption. For the electronic ground state X¹A₁ the adsorption minimum was found for the polar angle θ = 0°, which corresponds to a linear coordination of the CO adsorbate with the carbon atom down to the substrate surface. This is in contrast to the electronically excited state A³B₂, where the adsorption minimum was found for the polar angle θ = 180°, which describes a linear coordination with the oxygen atom of the CO molecule on top of the rutile TiO₂(110) surface. Moreover, this paper shows exemplary quantum dynamical calculations which simulate the laser-induced photodesorption as a first step to understand the desorption process in detail. Hence, higher dimensional calculations regarding more than 2 degrees of freedom of the CO molecule on the substrate surface are needed to get a complete description of this complex adsorbate–substrate system.

Keywords:

• ideal rutile(110) surface
• laser-induced photodesorption
• carbon monoxide
• electronically excited states
• ab initio potential energy surface

Acknowledgements

We like to thank Prof. Dr Bernd Meyer for providing the data of the relaxed coordinates from his embedded cluster model published in [12].

Notes

Note: ^aExponents and contraction coefficients optimised for Mg²⁺.