New X-ray technique unveils attosecond dynamics of electrons in liquid water

In a groundbreaking experiment reminiscent of stop-motion photography, scientists have achieved the remarkable feat of isolating the energetic movement of an electron while simultaneously “freezing” the motion of the much larger atom it orbits within a sample of liquid water.

Published in the esteemed journal Science, the findings represent a significant leap forward in our understanding of the electronic structure of molecules in the liquid phase, offering insights previously unattainable with conventional X-ray techniques. This innovative approach provides a new window into the immediate electronic response triggered when a target is bombarded with X-rays, thereby shedding light on the intricate effects of radiation exposure on both objects and living organisms.

Linda Young, a senior author of the research and Distinguished Fellow at Argonne National Laboratory, emphasizes the importance of unraveling the chemical reactions induced by radiation, which unfold on the incredibly fleeting timescale of attoseconds. Previously, radiation chemists were limited to resolving events at the picosecond timescale, a million times slower than an attosecond, akin to merely acknowledging the endpoints of a journey without comprehending the journey itself. With this breakthrough, scientists can now delve into the intricate processes occurring between birth and demise, unlocking a wealth of insights into radiation-induced chemistry.

A collaborative effort involving scientists from multiple Department of Energy national laboratories and universities in the U.S. and Germany, the research combines cutting-edge experiments with sophisticated theoretical models to unveil the real-time consequences of ionizing radiation interacting with matter.

By operating on the timescales where chemical transformations occur, the research team aims to deepen our understanding of complex radiation-induced chemistry, with implications ranging from nuclear waste management to medical diagnostics and treatment. This endeavor was made possible through the collaborative efforts of early-career scientists, who not only participated in the experiment but also contributed to the comprehensive analysis and interpretation of the data.

Carolyn Pearce, director of the IDREAM EFRC and a chemist at PNNL, underscores the invaluable role played by collaborative partnerships in advancing scientific discovery. The success of this endeavor underscores the transformative potential of interdisciplinary collaboration in tackling complex scientific challenges and unlocking new frontiers in our understanding of the natural world.

From the Nobel Prize to the field

Subatomic particles move with such incredible speed that capturing their movements demands a probe capable of measuring time in attoseconds—a timeframe so infinitesimally small that it dwarfs the entire history of the universe in terms of sheer quantity. This extraordinary feat of temporal resolution hinges on the burgeoning field of attosecond physics, which garnered the prestigious 2023 Nobel Prize in Physics for its groundbreaking contributions.

Harnessing the power of attosecond X-ray pulses, a capability available only at a select few specialized facilities worldwide, the research team embarked on their quest for unprecedented insights into the dynamic realm of atomic and molecular interactions. Conducting their experimental endeavors at the Linac Coherent Light Source (LCLS) within the SLAC National Accelerator Laboratory in Menlo Park, California, the team capitalized on the pioneering efforts of the local scientists who spearheaded the development of attosecond X-ray free-electron lasers.

Ago Marinelli, alongside James Cryan, played pivotal roles in crafting the synchronized pair of X-ray attosecond pump/probe pulses that propelled this experiment into uncharted territory. Marinelli emphasizes the significance of attosecond time-resolved experiments as a cornerstone of research and development at the Linac Coherent Light Source, heralding the exploration of new frontiers in attosecond science.

The innovative technique at the heart of this study—X-ray attosecond transient absorption spectroscopy in liquids—enabled the researchers to observe with unprecedented clarity the intricate dance of electrons energized by X-rays as they transition into an excited state. Crucially, this observation occurred before the bulkier atomic nucleus had time to react, providing a window into the fundamental dynamics of molecular processes.

Opting to investigate the behavior of liquid water—a ubiquitous yet remarkably complex substance—the researchers seized upon a captivating test case ripe with implications for diverse fields ranging from chemistry to biology. Through their pioneering efforts, they have unlocked a wealth of insights into the elusive realm of atomic and molecular dynamics, paving the way for future breakthroughs in our understanding of the microscopic world.

As attosecond science continues to push the boundaries of what is possible, these findings represent a testament to the ingenuity and collaborative spirit driving scientific discovery forward. By harnessing the power of attosecond pulses, researchers are poised to unravel the mysteries of the universe at a scale previously unimaginable, opening new vistas of exploration and discovery.

Source: Pacific Northwest National Laboratory

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