Amazing stuff!
"... The study provides evidence that excitation by light can enhance an atom's sensitivity to the motion of nearby atoms. The new method for following ultrafast chemical reactions at the atomic scale, in real time, can help researchers understand photostability in DNA, energy flow in light-harvesting materials and other fundamental processes driven by light.
The team investigated 3-fluoropyridine, a small ring-shaped molecule. When the molecule absorbs light like a short pulse from an ultraviolet laser, it is promoted into an electronically excited state and rapidly distorts out of its original planar shape. It then passes through a so-called conical intersection: a short-lived but crucial crossing point where movements of electrons and the atoms’ cores become strongly coupled. After this point, the molecule returns to the ground state.
At that moment, electronic energy is converted into vibrations.
The researchers found that this conversion leaves distinct fingerprints at different atomic sites: the fluorine atom acts as a clean marker of vibrational relaxation, while the nitrogen atom, which is more directly involved in the excitation, reflects an intertwined response of electron redistribution and structural motion. ..."
From the abstract:
"The advent of novel free-electron laser sources enabling time-resolved X-ray photoelectron spectroscopy (tr-XPS) provides a unique opportunity to monitor local chemical environments in real time by measuring sub-eV shifts in core-electron binding energies. These shifts reflect the interplay between electronic excitation and nuclear motion, an interplay that remains largely unexplored.
In our combined theoretical and experimental study of fluoropyridine (C5H4FN), we investigate this link by monitoring the evolving chemical environment at the N and F atomic sites as the photoexcited S1 state relaxes to the ground state via a conical intersection.
We find that the F site responds primarily to vibrational relaxation, showing minimal sensitivity to the electronic excited state.
In contrast, excitation to S1 induces a measurable energy shift at the N site and significantly enhances its sensitivity to local vibrations within the ring.
This behavior arises from a photoinduced redistribution of charge, which also increases the Coulomb interaction between the 1s electron at the N atom and the atomic partial charge at an adjacent C atom.
This insight opens new avenues for exploring ultrafast dynamics and conical intersection pathways in more complex systems, from photostable DNA bases to light-harvesting materials."
Researchers watch chemistry unfold atom by atom "Study suggests a new way to follow electronic and vibrational dynamics in real time"
Graphical abstract
Figure 1. Chemical shifts during conical intersection passage.
No comments:
Post a Comment