Light Makes a Surface Banana-Bond Split: Photodesorption of Molecular Hydrogen from RuO_2(110)

摘要

The coordination of H_2 to a metal center via polarization of its σ bond electron density, known as a Kubas complex, is the means by which H_2 chemisorbs at Ru~(4+) sites on the rutile RuO_2(110) surface. This distortion of electron density off an interatomic axis is often described as a 'banana-bond.' We show that the Ru-H_2 banana-bond can be destabilized and split using visible light. Photodesorption of H_2 (or D_2) is evident by mass spectrometry and scanning tunneling microscopy. From time-dependent density functional theory, the key optical excitation splitting the Ru-H_2 complex involves an interband transition in RuO_2 which effectively diminishes its Lewis acidity, thereby weakening the Kubas complex. Such excitations are not expected to affect adsorbates on RuO_2 given its metallic properties. Therefore, this common thermal cocatalyst employed in photocatalysis is, itself, photoactive.