Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Surface physics technique reveals complex chemical reactions on icy surfaces

26.08.2004


Dynamic ice

A technique borrowed from the surface physics community is helping chemists and atmospheric scientists understand the complex chemical reactions that occur on low-temperature ice.

Known as electron-stimulated desorption (ESD), the technique uses low-energy electrons to locally probe surfaces, differentiating their characteristics from those of the bulk material below them. Using ESD, researchers at the Georgia Institute of Technology have demonstrated that hydrochloric acid (HCl) quickly dissociates upon contact with icy surfaces – even at temperatures well below 100 degrees Kelvin, conditions seen naturally only in the outer solar system.



The work could lead to a better understanding of the complex atmospheric chemistry occurring in stratospheric ice crystals, the polar ice caps, aerosols containing ocean salt – and even the interface between water and DNA.

"These surface science techniques that have been established in the physics community for looking at the molecular structure of adsorbates on surfaces can also be applied to environmentally relevant problems," said Janine Herring-Captain, a doctoral student in Georgia Tech’s School of Chemistry and Biochemistry. "We can use them to get very basic information regarding some key environmental issues."

Using an ultra-high vacuum chamber, Herring-Captain used ESD to study HCl interactions with a variety of ice surfaces across a range of temperatures and pressures. The results of her work will be presented August 25th at the 228th National Meeting of the American Chemical Society in Philadelphia, PA. Information about the work, believed to be the first electron-energy, phase and temperature-dependent ESD study of cluster ion formation and HCl dissociation on ice surfaces, was published May 13 in Physical Review Letters.

Sponsored by the U.S. Department of Energy’s Office of Science, the work is part of a long-term study of electron collisions with complex targets and reactions on ice of various kinds – a material much more complex than it appears.

"As chemical physicists, we have to look at low temperature ice as a very dynamic surface. Ice is a stage for chemicals to meet each other and then react," said Thomas Orlando, co-author of the Physical Review Letters paper and chair of Georgia Tech’s School of Chemistry and Biochemistry. "This ice stage is intimately involved in the reactions, and without it, many reactions probably wouldn’t occur."

Even though extremely cold ice may seem like an improbable surface for many chemical reactions, water molecules in the outer one or two layers of ice remain in motion, even at temperatures found only in the outer solar system. On Earth, warmer ice surfaces are even more active.

"There are molecules moving onto and off of the surface, especially at the poles, where the temperatures are really warm compared to what we study in the laboratory," noted Herring-Captain. "Things are evaporating and re-condensing on the surface, which is where these atmospheric particles interact. Electron-stimulated desorption is an ideal way to study that surface activity."

Activity in these outer layers of ice can be dramatically different from what’s happening in the bulk.

"Most of the chemistry that is promoting the development of the ozone hole is happening at the surface because it is gas-phase molecules interacting with these dissolved species that may produce another gas," she noted. "Using ESD, we can de-couple the surface effects from what is going on in the bulk, which is what most people are seeing."

The research team, which also included Alex Aleksandrov, chose to study HCl interaction with ice because the protonation process is among the simplest reactions to take place. In their laboratory, they deposited very low concentrations of HCl onto icy surfaces at a variety of temperatures and pressures, and then focused 0.5 square millimeter electron beams on the surface to measure what was happening. Because the probe uses low-energy electrons, it did not significantly contribute to the reactions.

"Hydrochloric acid is supposed to be one of the reservoir species, but our research suggests it is never really there for long because the dissociation reaction takes place immediately," said Orlando. "The solvation happens almost instantly. We don’t think HCl is really ever a chemical entity available on the surface for reaction."

The dissociation effects occur at very low concentrations typical of those seen in atmospheric conditions. However, higher concentrations may change the dynamics, Orlando noted.

The extremely low temperatures and pressures achieved in their laboratory allowed the researchers to isolate the reactions they wanted to study from gas-phase effects that might occur at higher temperatures.

Because the studies were done at extremely low temperatures, the results have been controversial, Orlando admits.

"From a kinetics point of view, if these reactions are happening at low temperatures and low pressures, they must also be happening at higher temperatures and higher pressures," he said. "Few reactions slow down when the temperature rises and the higher temperatures and pressures are related to actual stratospheric conditions."

In related work, the research team is also studying formation of ion clusters from salt water and the interaction of electrons with DNA. Using a liquid jet injecting salt water into a vacuum, they found that the salt caused the water molecules to re-orient themselves at the interface, boosting the formation of ice clusters.

"When you think about salt and water, you expect to see a simple well-behaved solution," Orlando explained. "But at even low temperatures, salt and the associated solvation dynamics and structures are very complicated."

John Toon | EurekAlert!
Further information:
http://www.gatech.edu

More articles from Life Sciences:

nachricht Clock stars: Astrocytes keep time for brain, behavior
27.03.2017 | Washington University in St. Louis

nachricht Cryo-electron microscopy achieves unprecedented resolution using new computational methods
24.03.2017 | DOE/Lawrence Berkeley National Laboratory

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Electrical 'switch' in brain's capillary network monitors activity and controls blood flow

27.03.2017 | Health and Medicine

Clock stars: Astrocytes keep time for brain, behavior

27.03.2017 | Life Sciences

Sun's impact on climate change quantified for first time

27.03.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>