Quantum Calculations Reveal Ice’s Hidden Chemistry

Researchers at the University of Chicago Pritzker School of Molecular Engineering (UChicago PME), in collaboration with the Abdus Salam International Centre for Theoretical Physics (ICTP), have utilized quantum mechanical simulations to reveal how structural imperfections alter ice’s absorption and emission of light. The Trieste-Chicago collaboration employed advanced modeling approaches—developed to study materials for quantum technologies—to simulate four types of ice, including defect-free and imperfect crystal lattices. This research, published in Proceedings of the National Academy of Sciences, provides a new understanding of sub-atomic processes during ice melting and has implications for predicting greenhouse gas release from thawing permafrost.

Quantum Simulations Reveal Ice’s Chemical Behavior

Quantum simulations have revealed how imperfections within ice’s crystal structure significantly alter its absorption and emission of light. Researchers at UChicago PME and ICTP modeled ice with and without defects—vacancies, hydroxide ions, and Bjerrum defects—to understand decades-old observations of changing light absorption. These simulations demonstrated that each defect type creates a unique “optical signature,” allowing scientists to potentially identify them in real ice samples and explain previously unexplained experimental results.

The research team used advanced computational methods, originally developed for quantum technologies, to study ice at an unprecedented level. By simulating various defect types, they observed how UV light triggers the breakdown of water molecules into ions and radicals. The fate of these electrons—either spreading or becoming trapped—depends on the type of defect present. This level of control is impossible to achieve with physical ice samples, highlighting the power of computational modeling.

These findings have implications beyond fundamental physics, extending to climate change and astrochemistry. Understanding how UV light interacts with ice, particularly in thawing permafrost, is critical for predicting greenhouse gas release. The research could also shed light on chemical processes occurring on icy moons like Europa and Enceladus, where UV radiation drives molecular formation. The team is now working to validate their simulations with experimental measurements.

Impact of Defects on Light Absorption

Researchers discovered that imperfections within ice’s crystal structure dramatically alter how it absorbs and emits light. Simulations modeled defect-free ice alongside ice containing vacancies (missing water molecules), hydroxide ions, and Bjerrum defects (disrupted hydrogen bonding). Each defect type created a unique “optical signature,” like a fingerprint, influencing UV light absorption at different energies and explaining decades-old experimental observations of changing wavelengths. This level of precise control is unattainable with physical ice samples.

The research team demonstrated that the onset of UV light absorption varies depending on the presence of defects. Inserting hydroxide ions, for example, caused a shift in absorption energy compared to defect-free ice. Bjerrum defects resulted in even more significant changes, potentially explaining unexplained absorption features observed in ice exposed to prolonged UV radiation. These defects affect molecular-level changes—like the creation of hydronium ions, hydroxyl radicals, and free electrons—and how electrons spread or become trapped.

Understanding how defects influence light absorption is critical because it connects fundamental physics to real-world challenges. Better knowledge of ice melting and gas release under illumination can improve predictions of greenhouse gas release from thawing permafrost, impacting climate change modeling. The findings also have implications for understanding icy moons like Europa and Enceladus, where UV radiation drives chemical processes on ice-covered surfaces.

Decades-Old Puzzle of UV Light and Ice

For decades, scientists have puzzled over how ice absorbs ultraviolet (UV) light, noticing differing absorption patterns based on exposure time—minutes versus hours. Researchers proposed various chemical products might explain this change, but lacked tools for testing. New quantum mechanical simulations from the University of Chicago and ICTP reveal that imperfections within ice’s crystal structure dramatically alter how it absorbs and emits light, providing a potential explanation for these longstanding observations.

The research team simulated ice with and without defects—vacancies (missing water molecules), hydroxide ions, and Bjerrum defects (disrupted hydrogen bonding). They found each defect created a unique “optical signature” affecting UV light absorption. Notably, defect-free ice and ice with hydroxide ions showed differing absorption energies, mirroring the decades-old experimental findings. Bjerrum defects produced even more extreme changes, potentially explaining unexplained features in ice exposed to UV light for extended periods.

These findings have implications beyond fundamental physics, potentially improving predictions of greenhouse gas release from thawing permafrost. Understanding how sunlight interacts with ice is critical, as permafrost contains trapped gases. Additionally, this research could extend to understanding chemistry on icy moons like Europa and Enceladus, where UV radiation constantly impacts ice-covered surfaces and may drive molecular formation.

Implications for Climate Change and Astrochemistry

The research reveals connections between understanding ice chemistry and environmental challenges, specifically melting permafrost. As global temperatures rise and sunlight hits this permanently frozen ground, understanding how ice releases trapped greenhouse gases is critical for predicting climate change. Better knowledge of how ice melts and what it releases under illumination could significantly improve our understanding of these gas emissions, directly impacting climate models and predictions.

This work also extends to astrochemistry, potentially explaining chemical processes on icy moons like Jupiter’s Europa and Saturn’s Enceladus. UV radiation constantly bombards these ice-covered surfaces, and this research suggests it may drive the formation of complex molecules. The computational models developed can help scientists understand the photochemical reactions occurring on these distant, icy worlds, contributing to our broader understanding of chemistry beyond Earth.

The simulations demonstrated that defects within ice’s structure dramatically alter its light absorption properties. Researchers modeled ice with missing water molecules, charged ions, and structural disruptions, finding each defect created a unique “optical signature.” These signatures—observable changes in how ice absorbs and emits light—can now be sought in real ice samples, allowing experimental validation of the computational findings and providing a way to characterize ice’s composition.