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Physicists track the propagation of light in molecules-ScienceDaily



In the global competition for measuring time spans getting shorter and shorter, the physicists at Goethe University Frankfurt have now played a leading role: together with colleagues from the DESY accelerator facility in Hamburg and the Fritz-Haber Institute in Berlin, they measured a For the first time, the process is measured in seconds: the propagation of light within the molecule. One billionth of a second is one billionth of a billionth of a second (10-twenty one second).

In 1999, Egyptian chemist Ahmed Zewail won the Nobel Prize for measuring how quickly molecules change shape. He created flying chemistry using ultra-short laser flashes: the formation and destruction of chemical bonds occurs in the femtosecond range. Femtosecond is equal to 0.000000000000001

second or 10-15 second.

Now, the atomic physicists of the Goethe University (Reinhard Dörner) team have studied for the first time a process with an amplitude much shorter than femtoseconds. They measured the time it takes for a photon to pass through a hydrogen molecule: the average bond length of the molecule is about 247 milliseconds. This is the shortest time that has been successfully measured so far.

Scientists on the hydrogen molecule (H2), and then irradiated with X-ray laser source PETRA III at the Hamburg accelerator facility DESY. The researchers set the energy of the X-rays so that one photon is enough to expel two electrons from the hydrogen molecule.

Electrons appear as particles and waves at the same time, so the ejection of the first electron causes the electron wave to be emitted in one electron first, and then in the second hydrogen molecule atom in rapid succession, and the waves merge.

The photon here behaves like a flat pebble, passing twice on the water surface: when the trough meets the crest, the waves of the first water contact and the second water contact cancel each other out, thus forming a so-called interference pattern.

Scientists used the COLTRIMS reaction microscope to measure the first interference pattern of ejected electrons, a device that Dörner helped develop, which made the ultrafast reaction processes in atoms and molecules clearly visible. At the same time as the interferogram, the COLTRIMS reaction microscope can also determine the orientation of hydrogen molecules. The researchers here took advantage of the fact that the second electron also left the hydrogen molecule, so that the remaining hydrogen nuclei were scattered and detected.

“Since we know the spatial orientation of the hydrogen molecule, we use the interference of two electron waves to accurately calculate when the photon reaches the first hydrogen atom and when it reaches the second hydrogen atom,” Dr. Sven Grundmann explained. Theses constitute the scientific articles in Science. “This can be up to 247 milliseconds, depending on how far apart the two atoms are in the molecule from a light perspective.”

Professor Reinhard Dörner added: “We have observed for the first time that the electron shell in a molecule does not react to light anywhere at the same time. Since the information in the molecule only travels at the speed of light, there will be time. Delay. We have extended our COLTRIMS technology to another application.”

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