Scientists at SLAC National Accelerator Laboratory have successfully captured one of the fastest movements of a molecule called ferricyanide for the first time by combining two ultrafast X-ray spectroscopy techniques. They believe that their approach could help map more complex chemical reactions such as oxygen transportation in blood cells or hydrogen production using artificial photosynthesis.
The research team from SLAC, Stanford, and other institutions used a standard technique of zapping a mixture of ferricyanide and water with an ultraviolet laser and bright X-rays generated by the Linac Coherent Light Source (LCLS) X-ray free-electron laser. The ultraviolet light kicked the molecule into an excited state while the X-rays probed the sample’s atoms, revealing features of ferricyanide’s atomic and electronic structure and motion.
What was different this time is how the researchers extracted information from the X-ray data. Instead of studying only one spectroscopic region, known as the Kβ main emission line, the team captured and analyzed a second emission region, called valence-to-core, which has been significantly more challenging to measure on ultrafast timescales. Combining information from both regions enabled the team to obtain a detailed picture of the ferricyanide molecule as it evolved into a key transitional state.
The team showed that ferricyanide enters an intermediate, excited state for about 0.3 picoseconds—or less than a trillionth of a second—after being hit with a UV laser. The valence-to-core readings then revealed that following this short-lived, excited period, ferricyanide loses one of its molecular cyanide “arms,” called a ligand. Ferricyanide then either fills this missing joint with the same carbon-based ligand or, less likely, a water molecule.
“This ligand exchange is a basic chemical reaction that was thought to occur in ferricyanide, but there was no direct experimental evidence of the individual steps in this process,” SLAC scientist and first author Marco Reinhard said. “With only a Kβ main emission line analysis approach, we wouldn’t really be able to see what the molecule looks like when it is changing from one state to the next; we’d only obtain a clear picture of the beginning of the process.”
2023-05-06 14:00:03
Source from phys.org