X-ray laser reveals chemical reaction  

With the help of a so-called free electron x-ray laser, scientists have been able to follow in real time how bonds in a molecule are changed and broken and also found evidence of a much-discussed intermediate state before molecules bind to or leave a metal surface.

“To identify and characterise short-lived intermediate states in chemical reactions on metal surfaces has long been a dream,” says Henrik Öström at the Department of Physics, Stockholm University, who is part of the international research team that carried out the study.

“With the new free electron x-ray laser at SLAC, we have shown that dreams can become reality and managed to identify a short-lived intermediate state when the bindings of CO molecules to a metal surface are broken or created.

Powerful ultra-short (10-100 femtosecond) pulses of x-ray beams provided by the accelerator at the SLAC National Accelerator Laboratory provide the scientists with a snapshot of the electron distribution around the atoms of a molecule. By varying the delay between the start of a reaction and when the distribution of electrons is monitored with the x-ray pulse, the scientists were able to create a suspended-time image of changes in the course of the reaction.

“Scientists have long speculated whether such a state, a so-called ‘precursor’, exists. The new experiment is the first to directly show its existence,” says Lars G. M. Pettersson at the Department of Physics, Stockholm University. These studies will now go on to more complex reactions of interest to generating synthetic fuels, among other applications.

Besides the researchers from Stockholm University, scientists from Stanford University, SLAC, the University of Hamburg, the Technical University of Denmark, the Helmholtz Center in Berlin, and the Fritz Haber Institute in Berlin contributed to the study.

Published in Science