Observing a chemical reaction at the molecular level in real time is a major topic in experimental chemical physics. An international research team has captured roaming molecular fragments for the first time. The work, under the direction of Head Ibrahim, Research Assistant at the National Institute for Scientific Research (INRS) is published in the journal. Science.
The research group of the INRS Énergie Matériaux Télécommiation Research Center, with the support of Professor François Légaré, used the Advanced Laser Light Source (ALLS). They succeeded in filming the first ‘roving’ molecular film – hydrogen fragments, in this case – orbiting HCO fragments) during a chemical reaction by studying the photodegradation of formaldehyde, H2Tadalafil
Molecular road trip
“What we see in this new discovery is that, like on a road trip, the end target is unknown at first, and the path is not always straightforward. In general, particles, like humans, follow the easiest way to get from point A to point B. To reduce energy consumption, ”explains Hyde Ibrahim. “However, sometimes travelers may decide to take a slight detour.” Obviously the same applies to parts of molecules. This process is called roving, and was first discovered in formaldehyde molecules in 2004. Since then, indirect effects of wandering fragments called roving have been discovered in many molecular systems.
However, it was only recently that Dr. Ibrahim’s team was able to “catch them along the way” and capture them in real time. This is the first direct observation of the elusive wandering phenomenon observed so far. “It seems as though after the discovery of dinosaur footprints, a movie was discovered showing them walking around,” the researcher says.
In addition to wandering, there is also conventional dissociation, in which the molecule splits into parts upon excitation by ultrashort ultraviolet laser pulses. The parts can reach the same final products by following the direct paths (disintegration) or the indirect paths (roaming). “To do this work, one cannot simply wait for a shrapnel to reach the finish line, because this does not provide any information about the dynamics it went through. It was as if the road trip took place without a GPS and we couldn’t,” Heidi says. Ibrahim “Recover the route the travelers took.” To remedy this, the team found a way to identify a fragment that followed which path by placing checkpoints along the route; these towers act a bit like cell towers allowing the signal to be activated at a specific point along the route.
One of the many challenges in the experiments was related to the fact that the signal of these non-specific molecules occurs statistically. Imagine you want to take a photo of a traveler on the road, but you only have the name of the road and can pass at any time of the week. To add to the difficulty, the pilot signal is extremely fast (at a scale of 100 femtoseconds, or 10 billion times less than a millisecond) while it spans many times its size in time. Tomoyuki Endo, first author of the study, and a former INRS researcher now working at the Kansai Photon Science Institute (Japan), was able to follow “itinerants” using a technique called Coulomb Explosion Imaging (CEI).
Teams of Michael Shurman (National Research Council, Ottawa), Paul Houston (Cornell University, Ithaca, US) and Joel Bowman (Emory University, Atlanta, US) provided high-level theoretical support in all critical experimental stages.
“The results show that resolved CEI over time can bypass coherent molecular dynamics imaging – here, we follow statistical processes using conventional ultra-fast lasers,” says Professor Legari, director of the ALLS laboratory where the experiments were conducted. “In the near future, thanks to advances in high-repeat rate laser systems, it will be possible to study more complex particles.”
“Although roaming remains an elusive process that is difficult to comprehend, this scientific advance provides insight into how it is measured – as well as other statistical processes that require highly sensitive detection in the face of disruptive background signals,” says Hyde Ibrahim. “In the end, this may only be the beginning of another tortuous journey towards some of the secrets of Mother Nature; wandering is a process whose role in environmental and atmospheric chemistry is only at the beginning of understanding.”
Tomoyuki Endo et al, Real-time capture of wandering molecular fragments, Science (2020). DOI: 10.1126 / science.abc2960
Provided by the National Institute for Scientific Research – INRS
the quote: Researchers Capture Wandering Molecular Fragments in Real Time (2020, Dec 9) Retrieved December 9, 2020 from https://phys.org/news/2020-12-capture-roaming-molecular-fragments-real.html
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