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A new world record in short time measurement

Zeptoseconds: a new world record in short time measurement

The photon (yellow, coming from the left) produces electron waves from the electron cloud (gray) of the hydrogen molecule (red: nucleus), which interfere with each other (interference pattern: violet-white). The interference pattern is slightly curved to the right, which allows the calculation of the time it takes for a photon to travel from one atom to the next. Credit: Sven Grundmann, Goethe University Frankfurt

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999, 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.

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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More information:
Zeptosecond delay in birth by molecular photoionization, Science (2020). DOI: 10.1126 / science.abb9318

Provided by Goethe University in Frankfurt am Main

Quote: Zeptoseconds: A new world record in short time measurement (2020, October 16) extracted on October 16, 2020 from https://phys.org/news/2020-10-zeptoseconds-world-short.html

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