Breaking the chemical bonds in large molecules to form a desired substance can be a fiddly task, but simply chucking molecules at a wall can get the job done.
Stephan Rauschenbach at the University of Oxford and his colleagues made the discovery, which they call “splat chemistry”, after accidentally firing a complex molecule called Reichardt’s dye at a copper surface.
The team expected the collision to have enough energy to break all the bonds in the molecule, but that wasn’t the case, says Rauschenbach. “Despite this huge energy, it wasn’t just chaos, it was very selective.”
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Using a scanning tunnelling microscope to investigate the collision scene, the researchers noticed that the result wasn’t the mess they were expecting, but a more systematic crash. The molecule had “cracked” at a specific carbon-nitrogen bond, opening it up to a more spread-out formation. After running the experiment again, they found that the molecule split at this bond, creating two separate fragments.
The team created computer simulations of the collision and found that the molecule’s final state is based on its orientation as it hits the surface. Striking at a particular angle puts a strain on a particular bond and forces it to break. In contrast, during typical chemical reactions, molecules are heated, randomly distributing the energy without targeting specific bonds.
“We realised that molecular-surface collisions will divert energy to certain areas, and here we’re just exploiting it for a new type of mechanochemistry,” says team member Kelvin Anggara at the Max Planck Institute for Solid State Research, Germany.
This method opens up opportunities to create new molecules that cannot be made using conventional heating methods. “If someone could control the geometry of the molecule as it collides, you can get a controlled chemistry, and this is the dream for all chemists,” says Anggara.
Physical Review Letters
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