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New world record in short time measurement



Zeptoseconds: 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 interferes with each other (disruption pattern: violet white). The interference pattern slightly turns to the right, allowing the calculation of how long it takes for the photon 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 speed measurement in which molecules change their shape. He established femtochemistry using ultrashort laser flashes: the formation and breakdown of chemical bonds occurs in the field of femtoseconds.

Today, atomic physicists at Goethe University in Professor Reinhard Dörner’s team are for the first time studying a process shorter than femtoseconds by force. They measured how long a photon of a hydrogen molecule can cross: about 247 zeptoseconds for the average molecular bond length. This is the shortest time period that has been successfully measured so far.

Scientists perform a time measurement on a hydrogen molecule (H2) their X-ray beam from PETRA III X-ray laser source at the Hamburg accelerator facility DESY. The researchers set the X-ray energy so that one photon was sufficient to release both electrons from the hydrogen molecule.

Electrons act like particles and waves simultaneously, and therefore the emission of the first electron results in electrons waves being launched first into one, and then into the second hydrogen molecule at a rapid sequence. next, joining the waves.

The photon acts here like a flat pebble that is skimmed twice across the water: when a wave in the trough meets a vertex, the waves of first and second contact with water are each canceled, resulting in a so-called pattern of disruption.

Scientists measured the interference pattern of the first ejected electron using the COLTRIMS reaction microscope, a principle that Dörner helped develop and makes ultrafast reaction processes visible to atoms and molecules. Along with the disruption pattern, the COLTRIMS reaction microscopes also allowed the determination of the hydrogen molecule orientation. Researchers here have taken advantage of the fact that the second electron also left the hydrogen molecule, so that the remaining hydrogen nuclei will fly and be seen.

“Because we know the spatial orientation of the hydrogen molecule, we used the interference of two electron waves to accurately calculate when the photon reached the first and when the second hydrogen atom was reached,” Sven Grundmann explained that the doctor’s dissertation was forms the basis of the scientific article in Science. “And up to 247 zeptoseconds, it depends on how far between the molecules the two atoms are from the point of view of light.”

Professor Reinhard Dörner adds: “We observed for the first time that the electron shell in a molecule does not respond to light anywhere at the same time. Time delays occur because information inside the molecule only spreads at speed of light. In this search we have expanded our COLTRIMS technology to another application. ”


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Additional information:
Zeptosecond Birth Time Delay in Molecular Photoionization, Science (2020). DOI: 10.1126 / science.abb9318

Provided by Goethe University Frankfurt am Main



Citation: Zeptoseconds: New world record on short time measurement (2020, October 16) obtained on October 16, 2020 from https://phys.org/news/2020-10-zeptoseconds-world-short.html

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