The Attosecond Science group at the Center for Free-Electron Laser Science has made a major breakthrough with the development of a new light source capable of generating ultrafast UV pulses. This novel source allows scientists to investigate molecular dynamics triggered by ultraviolet light at an unprecedented temporal resolution, revealing insights into photochemical and photobiological processes at their earliest stages. A recent study from researchers at the University of Hamburg and DESY, published in Nature Communications, showcases how this technology opens new frontiers in understanding light-induced molecular changes.
When ultraviolet radiation interacts with molecules, such as those in DNA, it can trigger reactions that can lead to molecular damage or transformations. However, previous limitations in UV pulse duration hindered scientists’ ability to observe the ultrafast mechanisms that unfold in the initial femtoseconds following light absorption. These early moments are critical, as they capture the synchronized movement of electrons and nuclei, which ultimately shapes the molecule’s reactivity and response to UV light. Understanding molecular behavior in this narrow temporal window is essential to exploring new reaction pathways and potentially manipulating molecular processes.
In their research, the team aimed to determine whether it was possible to influence molecular reactivity by acting within a few femtoseconds—an incredibly brief timeframe in which electrons respond to UV excitation before the nuclei begin to move. To test this, they used the novel light source on iodomethane, a model molecule in ultraviolet spectroscopy, to observe its behavior within a 5-femtosecond window after excitation. The researchers discovered that applying a second laser pulse within this window could halt the molecule’s fragmentation, an observation that had not been possible before due to the longer duration of traditional UV pulses.
Francesca Calegari, head of the Attosecond Science group and a lead scientist at DESY, explained that this second pulse offers a form of molecular intervention: without it, the molecule would inevitably dissociate. The team’s findings validate theoretical models of molecular response to UV light, providing insights into the precise timing of events like reaching the critical carbon-iodine bond distance where two electronic states can exchange populations. Co-author Vincent Wanie highlighted that this combination of experimental and theoretical work marks a new approach to manipulating molecular behavior immediately after photoexcitation.
This breakthrough demonstrates a form of photoprotection that prevents molecular dissociation, which could have far-reaching implications. Scientists envision that this technology could be adopted across various fields to study critical UV-triggered phenomena, from photochemistry to photobiology. By enabling precise manipulation of molecular reactions, the new UV pulse source could lead to advancements in areas like photocatalysis and drug design, where controlling photoproducts is key.
Source: University of Hamburg