An international research team led by the Politecnico di Milano has built an apparatus that can follow a molecule in the very first instants after it absorbs light, tracking the coordinated motion of electrons and nuclei with a temporal resolution of just three femtoseconds. The platform, described in a study published in Nature Communications as part of the European ERC Synergy TOMATTO project, places the instrument among the world leaders in time-resolved photoelectron spectroscopy. One femtosecond is one millionth of one billionth of a second, and resolving events at this scale makes it possible to separate stages of photochemical reactions that earlier instruments could not distinguish in time.
The apparatus works by synchronising two extremely short light pulses with exceptionally high precision. The first pulse, in the ultraviolet, is absorbed by the molecule and initiates its evolution. The second pulse, in the extreme ultraviolet and lasting only a few attoseconds, reaches the molecule after a controllable time interval and allows the researchers to reconstruct its state at that precise moment. By repeating the measurement at successive intervals, the team can track the redistribution of energy and the joint motion of electrons and nuclei as the light-triggered transformation unfolds. The beamline architecture integrates ultrashort UV pulses and attosecond XUV pulses into a single platform, enabling photoelectron spectroscopy measurements with extreme temporal resolution.
To demonstrate the capabilities of the new method, the researchers studied acetylacetone, a molecule used as a model for understanding how light can trigger ultrafast transformations. Thanks to the precision achieved, it was possible to distinguish two successive passages through a conical intersection, a crucial junction at which the molecule changes electronic state and is directed towards a specific transformation pathway. These are phenomena that previously available instruments were unable to separate in time. In the case of acetylacetone, the experiment made it possible to reconstruct the initial stages of the transformation triggered by light in unprecedented detail.
“With this apparatus, we can follow a molecule in the very first instants after it absorbs light, with a level of detail that was not previously accessible. It is like vastly increasing the number of frames in a film: a seemingly single transformation finally reveals all its intermediate stages,” says Mauro Nisoli, professor at the Department of Physics of the Politecnico di Milano and coordinator of the ERC Synergy TOMATTO project. “What we observe is the moment when light sets the molecule in motion and reorganises its internal energy,” explains Maurizio Reduzzi, Associate Professor at the Department of Physics of the Politecnico di Milano. “Being able to follow these stages directly means getting closer to the heart of photochemical processes, where a transformation truly takes shape.”
The ability to change the wavelength of the ultraviolet pulse makes the apparatus suitable for studying different molecules and electronic states. According to the researchers, the method may therefore be applied to more complex systems, from molecules of biological interest to photoactive materials and processes linked to energy conversion. The platform also opens up new prospects for attochemistry, the field of research that studies the possibility of observing and, in the future, controlling chemical transformations by acting on the motion of electrons before the slower motion of atoms begins. The study was carried out by researchers from the Politecnico di Milano, the Institute for Photonics and Nanotechnologies of the CNR, Heriot-Watt University in Edinburgh and the University of Bologna, with the support of the European Research Council through the ERC Synergy TOMATTO project. The study, by M. Pini and colleagues, is titled “3-fs-resolved UV/XUV photoelectron spectroscopy in the gas phase” and was published in Nature Communications.
Subject of Research: Ultrafast UV/XUV photoelectron spectroscopy of light-triggered molecular transformations
Article Title: Three femtoseconds to observe a molecule as it changes
Article References: Three femtoseconds to observe a molecule as it changes. Original publication (Bibliographic details unavailable.)
Image Credits: AI Generated
DOI: Not provided
Keywords: femtosecond spectroscopy, attosecond pulses, photochemistry, conical intersection, acetylacetone, photoelectron spectroscopy, attochemistry, Politecnico di Milano, ERC Synergy TOMATTO, Nature Communications, ultrafast dynamics, extreme ultraviolet
News Source: Bethany Barker. (October 29, 2026). New apparatus tracks molecular changes with three-femtosecond resolution. Scienmag.
