Researchers observed a chemical bond being born for the first time in history.
Using an X-ray laser at the Department of Energy's SLAC National Accelerator Laboratory, scientists caught their first glimpse of the transition state in which two atoms begin to form a weak bond in the first steps of transforming into a molecule.The observations provide insight into how chemical reactions occur, and could lead to new breakthroughs in efforts to design reactions that produce energy.
"This is the very core of all chemistry. It's what we consider a Holy Grail, because it controls chemical reactivity," said Anders Nilsson, a professor at the SLAC/Stanford SUNCAT Center for Interface Science and Catalysis and at Stockholm University who led the research. "But because so few molecules inhabit this transition state at any given moment, no one thought we'd ever be able to see it."
The research team looked at the same reaction that neutralizes carbon monoxide (CO) from car exhaust in a catalytic converter; but in this case the reaction took place on the surface of a catalyst that holds C) and oxygen atoms together, allowing them to link up more easily and form carbon dioxide. The pulse of the laser heated this catalyst to 2,000 kelvins (over 3,000 degrees Fahrenheit) which also increased the chances of the atoms knocking into each other and forming a connection.
The X-ray laser pulses from SLAC's Linac Coherent Light Source (LCLS) allowed the team to observe this process by detecting changes in the arrangement of the atoms' electrons that occurred in quadrillionths of a second.
"First the oxygen atoms get activated, and a little later the carbon monoxide gets activated," Nilsson said. "They start to vibrate, move around a little bit. Then, after about a trillionth of a second, they start to collide and form these transition states."
The researchers were surprised to observe that many of the reactants entered a transition state, but only a small amount formed stable carbon dioxide without breaking apart.
"It's as if you are rolling marbles up a hill, and most of the marbles that make it to the top roll back down again," Nilsson said. "What we are seeing is that many attempts are made, but very few reactions continue to the final product. We have a lot to do to understand in detail what we have seen here."
The team is now working to measure transition state in other catalytic reactions that can generate commercially-valuable chemicals.
"This is extremely important, as it provides insight into the scientific basis for rules that allow us to design new catalysts," said SUNCAT Director and co-author Jens Nørskov.
The findings were published in a recent edition of the journal Science Express.
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