Photodissociation Dynamics in Vacuum Ultraviolet Spectroscopy

Photodissociation dynamics in the vacuum ultraviolet (VUV) region investigates how molecules absorb high‐energy photons and undergo bond cleavage into reactive fragments. When a molecule is irradiated in the VUV (100–200 nm), it is promoted to excited electronic states that may be bound, repulsive or predissociative. The ensuing competition between radiative decay, nonadiabatic transitions and spin–orbit coupling dictates branching ratios into distinct product channels. Detailed understanding relies on combining synchrotron‐based photoabsorption, time‐resolved pump–probe measurements and high‐level quantum‐chemical potential‐energy surfaces. Studies of simple diatomics such as N₂ and CO have revealed oscillatory energy‐dependent yields, isotope effects and the role of Rydberg and valence state manifolds. Insights into these mechanisms underpin models of upper‐atmosphere chemistry, astrochemical environments and isotope fractionation in planetary systems, and inform the development of attosecond‐scale spectroscopic probes.

Research from Nature Portfolio

Recent studies have demonstrated a pronounced isotope‐dependent branching in the VUV photodissociation of carbon monoxide. By measuring quantum yields for ^12C^16O versus ^13C^16O in the Rydberg complex region, researchers revealed that rare isotopologues exhibit dramatically shifted absorption lines and oscillator strengths, leading to stark differences in fragment yield. The work showed that specific electronic states govern the production of excited C atoms, emphasising that photochemical models of solar‐system and interstellar environments must incorporate state‐resolved isotope effects to predict fractionation accurately.

Photodissociation Dynamics in Vacuum Ultraviolet Spectroscopy publication trend

The graph below shows the total number of articles in photodissociation dynamics in vacuum ultraviolet spectroscopy across all publications each year (not limited to Nature Index journals).

Technical terms

Photodissociation: The process by which a molecule absorbs a photon and breaks into two or more fragments.

Vacuum ultraviolet (VUV): The ultraviolet spectral region from about 10 to 200 nm, often requiring specialised sources such as synchrotron radiation.

Branching ratio: The relative probability of a photodissociation event yielding one set of products versus another.

Nonadiabatic coupling: Interaction between electronic states that enables transitions during nuclear motion.

Spin–orbit coupling: Quantum mechanical interaction mixing electronic spin and orbital angular momentum, facilitating intersystem crossing.

Rydberg state: An excited electronic state of a molecule in which an outer electron occupies a high principal quantum number orbital.

References

1. On the Energy-specific Photodissociation Pathways of 14N2 and 14N15N Isotopomers to N Atoms of Different Reactivity: A Quantum Dynamical Perspective. The Astrophysical Journal (2023).
2. Strong and selective isotope effect in the vacuum ultraviolet photodissociation branching ratios of carbon monoxide. Nature Communications (2019).
3. Nonadiabatic dynamics in a forest of coupled states: Electronic state branching in the VUV photodissociation of N2. The Journal of Chemical Physics (2023).