If you truly want to understand the dynamics of a chemical reaction, you’ve got to observe it very closely. That means observing the movement of atoms and molecules, at a time scale to match. Here are a few ranges from the atomic time scale:
- Rotation of molecules: picoseconds (10-12 s)
- Vibration of atoms: femtoseconds (10‑15 s)
- Movement of electrons: attoseconds (10-18 s)
That’s some pretty fast movement. But researchers at ETH Zurich, a science and engineering university in Switzerland, have succeeded in generating the world’s shortest laser pulse with a duration of 43 attoseconds. That means they can now observe in high detail the movement of electrons within a molecule, and the formation of chemical bonds.
As published in the journal Optics Express, the researchers start a soft X-ray laser pulse from an infrared laser, giving it a very large spectral bandwidth. This allows them to excite the inner-shell electrons of elements present in biomolecules, such as phosphorus and sulfur, and to directly observe them with unprecedented time resolution.
One application of attosecond laser spectroscopy could be the development of more efficient solar cells: The technology makes it possible to follow the step-by-step process of excitation through sunlight up to the generation of electricity. Gaining a detailed understanding of the charge transfer pathway could help optimize the efficiency of next-generation photosensitive elements.
And it’s not just observation we’re talking about; the technology makes it possible to directly manipulate chemical reactions. Chemical bonds, for instance, can be broken by using the laser pulse to stop the charge shift at a certain location in the molecule. Targeted interventions like this have previously been impossible, because the electron-movement time scale was beyond reach.
The researchers, led by ETH Prof. Hans Jakob Wörner, are currently working on even shorter laser pulses that will make it possible to record even more detailed images. A wider X-ray spectrum will also make it possible to probe even more elements, and follow the migration of electrons in more complex molecules.