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Physicists track the propagation of light into a molecule – ScienceDaily



In the global race to measure shorter and shorter intervals, physicists at Goethe University in Frankfurt have already taken the lead: together with colleagues at the DESY accelerator in Hamburg and the Fritz-Haber Institute in Berlin, they measured a process that hides in the realm of zeptoseconds for the first time: the propagation of light in the molecule. The zeptosecond is the trillionth of a billionth of a second (10-21 seconds).

In 1999, Egyptian chemist Ahmed Zewail received the Nobel Prize for measuring the rate at which molecules change shape. He founded femtochemistry using ultrashort laser flashes: the formation and disintegration of chemical bonds occurs in the realm of femtoseconds. The femtosecond is equal to 0.00000000000000001

seconds or 10-15 seconds.

Now, atomic physicists at Goethe University, under the team of Professor Reinhard Dörner, have for the first time studied a process that is shorter than femtoseconds in magnitude. They measured how long it takes a photon to cross a hydrogen molecule: about 247 zeptoseconds for the average bond length of the molecule. This is the shortest period of time that has been successfully measured so far.

Scientists have measured time on a molecule of hydrogen (H2), which are irradiated with X-rays from the X-ray laser source PETRA III in the Hamburg accelerator DESY. The researchers determined the energy of the X-rays so that one photon was enough to eject the two electrons from the hydrogen molecule.

Electrons behave as particles and waves simultaneously, and therefore the ejection of the first electron resulted in electron waves being fired first into one and then into a second atom of a hydrogen molecule in rapid succession, as the waves merged.

The photon behaved here much like a flat pebble that is carried twice through water: when the trough of a wave meets a wool crest, the waves of the first and second water contact are annulled, leading to the so-called interference pattern.

Scientists have measured the interference pattern of the first ejected electron using the COLTRIMS reaction microscope, a device that Dörner helped develop and that makes ultrafast reaction processes in atoms and molecules visible. Simultaneously with the interference model, the COLTRIMS reaction microscope also allows the determination of the orientation of the hydrogen molecule. The researchers here took advantage of the fact that the second electron also left the hydrogen molecule, so that the remaining hydrogen nuclei separated and were discovered.

“Because we knew the spatial orientation of the hydrogen molecule, we used the interference of the two electron waves to calculate exactly when the photon reached the first and when it reached the second hydrogen atom,” explains Sven Grundman, whose doctoral dissertation is the basis of a scientific paper in Science. “And that’s up to 247 zeptoseconds, depending on how far apart the two atoms were in terms of light.”

Professor Reinhard Dörner added: “For the first time, we have noticed that the electron shell in a molecule does not react everywhere at the same time to light. The time delay occurs because the information in the molecule propagates only at the speed of light. COLTRIMS technology to another application. “

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Materials provided by Goethe University in Frankfurt. Note: Content can be edited for style and length.


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