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New world record in short time measurement



Zeptose seconds: new world record in short time measurement

The photon (yellow coming from the left) produces electron waves out of the electron cloud (gray) of the hydrogen molecule (red: nucleus) that interferes with each other (interference pattern: violet-white). The interference pattern is slightly skewed to the right, making it possible to calculate how long the photon is required to get 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 their shape. He founded femtochemistry using ultra-short laser flashes: the formation and division of chemical bonds occurs within femtoseconds.


Now, for the first time, nuclear physicists at Goethe University in Professor Reinhard Dörner’s team have studied a process that is shorter than femtoseconds in order of magnitude. They measured how long it takes for a photon to cross a hydrogen molecule: approx. 247 zeptose seconds for the average binding length of the molecule. This is the shortest time period that has been measured to date.

The researchers performed the time measurement on a hydrogen molecule (H2) which they irradiated with X-rays from the X-ray laser source PETRA III at Hamburg’s accelerator system DESY. The scientists put the energy from the X-rays so that one photon was sufficient to push both electrons out of the hydrogen molecule.

Electrons behave like particles and waves simultaneously, and therefore the ejection of the first electron resulted in electron waves, which were launched first in one and then in the other hydrogen molecule atom in rapid succession, with the waves intertwined.

The photon behaved here much like a flat pebble that dusks twice over the water: when a wave trough meets a wave crest, the waves from the first and second water contacts cancel each other out, resulting in what is called an interference pattern.

The researchers measured the interference pattern of the first ejected electron using the COLTRIMS reaction microscope, an apparatus that Dörner helped develop that visualizes rapid reaction processes in atoms and molecules. Simultaneously with the interference pattern, the COLTRIMS reaction microscope also allowed 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 flew apart and were detected.

“Knowing 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 Grundmann, whose doctoral dissertation forms the basis of the scientific article in Science. “And this is up to 247 zeptose seconds, depending on how far apart in the molecule the two atoms were from the perspective of light.”

Professor Reinhard Dörner adds: “We observed for the first time that the electron shell of a molecule does not react to light everywhere at the same time. The time delay occurs because information inside the molecule is only spread at the speed of light. for another application. ”


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More information:
Zeptose second delay in molecular photoionization, Science (2020). DOI: 10.1126 / science.abb9318

Provided by Goethe University Frankfurt am Main

Citation: Zeptose seconds: New world record in short time measurement (2020, October 16) retrieved October 16, 2020 from https://phys.org/news/2020-10-zeptoseconds-world-short.html

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