Ultrafast electron imaging captures never-before-seen nuclear motion in hydrocarbon molecules excited by light
The researchers used a genetic algorithm to obtain the time-varying molecular structure of photoexcited o-nitrophenol from ultrafast electron diffraction data. Credit: JPF Nunes (generated using Microsoft Copilot)
Interactions between light molecules and nitroaromatic hydrocarbon molecules have important effects on chemical processes in the atmosphere that can cause smog and pollution. However, changes in molecular geometry due to interaction with light can be very difficult to measure as they occur on sub-angstrom length scales and femtosecond time scales.
In a study published in the journal Physical Chemistry Chemical Physics, researchers used an ultrafast electronic camera to image the movement of hydrocarbon molecules at a scale of 1/10,000 times the width of a human hair.
This ultra-precise and ultra-fast imaging technique, supported by advanced calculations, reveals the proton transfer step and subsequent out-of-plane twisting motion as key components of energy relaxation. (Relaxation is the process by which a molecule moves from an excited, high-energy state to a lower-energy ground state after absorbing light.)
Previous studies have proposed various ways for hydrocarbon molecules to relax after interacting with light. However, scientists lacked experimental data to verify what kind of process occurred.
In this study, the scientists used a relativistic ultrafast electron diffraction (UED) instrument to observe the relaxation of photoexcited o-nitrophenol. We then used a genetic structure-fitting algorithm to extract new information from the UED data about small changes in molecular shape that were unrecognizable in previous studies.
Specifically, this experiment resolved key processes in the relaxation of o-nitrophenol: proton transfer and deplanarization (i.e., rotation of part of the molecule out of the molecular plane). Non-empirical multiple spawning simulations confirmed the experimental results.
The researchers were able to identify a key relaxation pathway involving proton transfer and molecular ‘kinking’. The results lay the groundwork for studying more complex molecules that scientists believe have similar interactions. It also helps researchers better understand how contamination occurs.
Further information: JPF Nunes et al, Photoinduced structural dynamics of o-nitrophenol by ultrafast electron diffraction, physical chemistry, chemical physics (2024). DOI: 10.1039/D3CP06253H
Provided by the U.S. Department of Energy
Citation: Ultrafast electron imaging captures unprecedented nuclear motion in hydrocarbon molecules excited by light (December 10, 2024) https://phys.org/news/2024-12-ultrafast-electron -imaging- Retrieved on December 10, 2024 from capture-nuclear.html
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