For the first time, an international scientists' team observed the volatile intermediate stages which appear when carbon monoxide oxidises on a hot ruthenium surface, an ordinary catalyst. The scientists, including researchers from the University of Hamburg and DESY, used the ultra-short X-ray flashes of the X-ray laser LCLS at the research centre SLAC in California. Initially, an optical laser pulse heated the ruthenium surface, thus activating the absorbed carbon monoxide molecules and oxygen atoms. With the help of X-ray absorption spectroscopy, the team was able to detect how the electronic structure of the involved oxygen atoms changed during the formation of carbon dioxide molecules – a process which regularly takes place in a similar way in all automobile catalysts. The observed transition states assort well with quantum chemical calculations.