Visualising sigma orbitals opens path to new understanding of surface chemistry

A technique developed for imaging π orbitals during surface chemical reactions – photoemission orbital tomography – can also image σ orbitals as well. The researchers, who tested their discovery by answering a hitherto open question about the product of a reaction, believe the method could unravel chemical mechanisms in fields such as catalysis.

Surface chemistry is crucial to fields such as heterogeneous catalysis and microfluidics. To understand chemical structures, researchers often use scanning tunnelling microscopy to measure the depths of electrons’ potential wells. Unfortunately, this only works for very loosely bound electrons, which are usually in π orbitals, as applying too much voltage causes the junction between the tip and the surface to become unstable. However, other electrons are important in bonding too. ‘For example only σ orbitals are involved in bonding to hydrogen atoms, because the hydrogen atom has an s-like orbital that can only attach to a σ orbital,’ explains theoretical physicist Peter Puschnig at the University of Graz in Austria.