First step taken to image ultra-fast movements in chemical reactions

A team of international researchers have fired ultra-fast shots of light at oxygen, nitrogen and carbon monoxide molecules as part of a development aimed at mapping the astonishingly quick movements of atoms within molecules, as well as the charges that surround them.

The ultra-short laser that spans only a few hundred attoseconds -- an attosecond is equivalent to one quintillionth of a second -- was fired in a sample of molecules and could pave the way towards imaging the movement of atoms and their electrons as they undergo a chemical reaction -- one of the holy grails of chemistry research.

This latest study has been published today, 16 March, as part of a special issue on attosecond science, in IOP Publishing's Journal of Physics B: Atomic, Molecular and Optical Physics to mark the 10th anniversary of the first ever attosecond laser pulse.

Previous research has been able to probe the structure of molecules using a variety of techniques; however, the inherent challenge is to perform these experiments in systems where changes are rapidly occurring on very small time scales.

The researchers used two lasers in their experiments: the first held the molecule in place whilst the second was fired at it. The second laser operated in the extreme ultra-violet region of the electromagnetic spectrum as this is one of only two regions -- x-ray being the other -- where the laws of physics allow laser pulses to be produced on an attosecond timescale.

Once the target molecule was in place, short pulses of the laser were fired at in an attempt to dislodge an electron. This process, known as photoionization, allows atoms and molecules to be imaged in unprecedented detail as the ejected electrons carry crucial information about where it came from.

In this experiment, the samples, which existed as a gas, were stable, meaning no reactions were taking place; however, the major goal of the research team is to monitor the electrical and molecular changes, in real-time, that occur as atoms undergo a chemical reaction.

They intend to do this by triggering a reaction with the laser, breaking a chemical bond that holds molecules together, and then using the described technique to image the changes that occur in the molecule as they happen.

Lead author of the study Dr Arnaud Rouzée from the Max-Born-Institute said: "We show that the photoelectron spectra recorded for a small molecule, such as oxygen, nitrogen and carbon monoxide contains a wealth of information about electron orbitals and the underlying molecular structure.

"This is a proof-of-principle experiment that electrons ejected within the molecule can be used to monitor ultrafast electronic and atomic motion."

Story Source:

The above story is reprinted from materials provided by Institute of Physics (IOP), via AlphaGalileo.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Arnaud Rouzée, Freek Kelkensberg, Wing Kiu Siu, Georg Gademann, Robert R Lucchese, Marc J J Vrakking. Photoelectron kinetic and angular distributions for the ionization of aligned molecules using a HHG source. Journal of Physics B: Atomic, Molecular and Optical Physics, 2012; 45 (7): 074016 DOI: 10.1088/0953-4075/45/7/074016

Glass from the past informs decisions for the future

The local electrode atom probe – a $1.6 million atom probe tomography system referred to as “LEAP” – is enabling EMSL users Denis Strachan and Joseph Ryan, both with Pacific Northwest National Laboratory, to obtain atom-by-atom views of how glass corrodes over time.

Located at EMSL, LEAP was purchased with American Recovery and Reinvestment Act funds. It’s the first analytical tool of its kind available to the global scientific community in a user facility. LEAP offers unprecedented 3-D chemical imaging of metals, and it’s currently being developed to analyze low electrical conductivity materials, such as ceramics, semiconductors and oxides. Discovering the most fundamental properties of these materials can lead to new technological innovations.

NOW AND LATER

Scientists use LEAP for a wide variety of experiments. In this case it is directly related to an environmental cleanup mission at the Department of Energy’s Hanford Nuclear Reservation near PNNL.

At Hanford, the DOE is building an immense facility devoted to vitrification – the process of containing radioactive waste by transforming it into highly durable glass for long-term storage. To support safety both for present and future generations, scientists like Strachan, Ryan and other top researchers worldwide are using sophisticated instruments and computer models to help understand how glass will behave over the long term, up to 1 million years.

Glass dissolves very slowly, which is a major reason it’s being used to store radioactive waste. However, this advantage also presents a challenge. It’s difficult to perform experiments over sufficiently long periods to gather the results scientists need to refine the computer simulations used to calculate the behavior of vitrified waste stability over thousands of years.

Studying how glass dissolves requires sophisticated instrumentation and ancient glass. The longest test on a piece of human-made, simulated nuclear-waste glass has been about 25 years. So Strachan and Ryan sought out collaboration with EMSL and Italian scientists to analyze Roman glass artifacts collected recently in Italy. Modern technology created advanced capabilities, such as LEAP, to effectively investigate these artifacts.

THE ILL-FATED IULIA FELIX

One source of the ancient glass was the Iulia Felix, a common merchant ship called a corbita that shipwrecked in the northern Adriatic Sea in the second or third century AD. The roughly 50-foot-long ship was carrying a barrel containing about 11,000 pieces, or about 309 pounds, of glass for recycling and containers holding oils and spices. Early in 2011, the PNNL team worked with the University of Padua in Italy to obtain samples of glass recovered from the Iulia Felix. They also recovered glass still in contact with soil from an 1,800-year-old Roman villa in the nearby town of Aquileia. In addition, they are collaborating with French scientists to study a third glass sample of about the same age from a shipwreck off the southern coast of France, near the island of Embiez.

At EMSL, the researchers are using LEAP and focused ion beam sample preparation techniques to give them the experimental data needed to properly interpret the results of these 1,800-year-long experiments. With the first round of experiments, unforeseen findings have already surfaced related to the glass structure and durability.

“Our very first analyses showed previously undetected nanoscale segregation of magnesium into layers that are roughly two nanometers thick,” said Ryan. “We expect to find even more surprises as we continue to interpret the data in more detail.”

Detailed data like these, drawn from an experiment nearly 2,000 years in the making, are then integrated with computational models to improve simulations of glass dissolution. The techniques used in these studies are already being applied to corroded simulated waste glasses to allow precise comparisons between the different types of glass. Further results will allow engineers to use the incredible durability of vitrified waste with confidence when designing repositories.

As a byproduct of this research, archaeologists will also benefit by having more information about how glasses interact with water.

Provided by Environmental Molecular Sciences Laboratory (news : web)

Novel plastics and textiles from waste with the use of microbes

"By means of gene technology, we can modify microbial metabolism and thereby produce organic acids for a wide range of industrial applications. They can be used, among other things, for manufacturing new plastic and textile materials, or packaging technologies," explains Merja Penttilä, Research Professor and Director of the Centre of Excellence from VTT Technical Research Centre of Finland.

New methods play a key role when various industries are developing environmentally friendly and energy-efficient production processes. Use of renewable natural resources, such as agricultural or industrial waste materials, to replace oil-based raw materials will make industries less dependent of fossil raw materials and, consequently, reduce carbon dioxide emissions into the atmosphere.

The CoE also develops highly sensitive measuring methods and investigates microbial cell functions at molecular level. "We need this information to be able to develop efficient bioprocesses for the future. For instance, we build up new micro- and nanoscale instruments for measuring and controlling microbial productivity in bioreactors during production."

Alternatives for oil

The metabolism of microbes is modified so that they will convert plant biomass sugars into sugar acids and their derivatives. These compounds can potentially serve as raw materials for new types of polyesters, whose properties – such as water solubility and extremely rapid degradation into natural substances – can be used, for example, in medicine. By modifying sugar acids, it is also possible to produce compounds that may replace oil-based aromatic acids in the manufacture of thermosetting plastics and textiles.

"Sugar acids can be used to produce biodegradable technical plastics, including polyamides, or functional components that increase the ability of cellulose to absorb water. Novel materials could replace the currently available non-biodegradable absorbent components in hygiene products. Sugar acids are also a source of hydroxy acids, such as glycolic acid, whose oxygen-barrier properties make it suitable for food packaging," explains Professor Ali Harlin, the head of the CoE Green Chemistry team.

In order to be able to replace, in the future, industrial production that is based on petrochemicals with new production processes based on waste biomass, such new processes must be extremely efficient. "A major challenge is how make the production organisms used in bioprocesses, that is, the microbes, to utilise the sugars of the biomass and to convert them into desired compounds in the most effective manner. This development work calls for multidisciplinary competence ranging from biosciences to engineering."

Provided by Academy of Finland

How nitric acid overcame its fear of water with a little help from its friends

A collaborative team of theorists and experimentalists from Pacific Northwest National Laboratory, University of California at Irvine and Helmholtz-Zentrum Berlin for Materials and Energy, also providing a light source used in the experiments, joined together to obtain these results.

How do you stop smog without halting the economy? That's a question near and dear to the hearts of leaders in the scientific, industrial, and political communities. To find ways to deal with the nitric acid in smog, we must first understand if key reactions involve the acid or its dissociated products. If the reactions involve some of each, how much? Knowing what is happening at the fundamental level gives scientists and other stakeholders the right foundation to move forward. Further, nitric acid is a common prototype that is a good starting point for dissociation studies.

Researchers analyzed the behavior of nitric acid in water. Did it dissociate at the interface or stay together? How about deeper into the water? The team used x-ray photoelectron spectroscopy. The instruments offered data on the concentration of the nitric acid and its dissociation product, nitrate or NO3-. The scientists saw evidence that nitric acid stayed together more at the interface than they expected, even under conditions where it should have readily dissociated.

To determine what was happening during the experiment, Dr. Christopher Mundy and Linus Pauling Postdoctoral Fellow Dr. Marcel Baer at PNNL performed the first principles molecular simulations and together with UC Irvine's Prof. Doug Tobias and postdoctoral fellow Dr. Abe Stern analyzed the results.

"The experiment cannot see the molecules, but the theorists can," said Mundy.

The theory team used large, complex calculations to simulate the nitric acid and water system. They modeled the acid at the surface of water, known as the air/water interface. Further, the team examined the molecules just slightly below the interface and in the bulk water. The size of the calculations demanded time on supercomputers, which was granted by the U.S. Department of Energy's INCITE effort and other resources. With these calculations, the team could see hydrogen bonds forming and breaking.

The team took the results from the simulations and compared them to the experimental results. The simulations explained the different experimental data. "At higher concentrations, nitric acid will pick up a hydrogen bond without dissociating. This correlates quite well to the experimental data," said Baer.

The bonds created a support structure for the nitric acid, reducing dissociation. The results back up other studies that indicate nitric acid dissociates less at the interface then it does in bulk water.

The theoretical chemistry team at Pacific Northwest National Laboratory is continuing to perform highly detailed calculations to get a better view of ions' behavior at interfaces. This work is an important part of the national laboratory's portfolio of research for the U.S. Department of Energy.

More information: T Lewis, et al. 2011. "Does Nitric Acid Dissociate at the Aqueous Solution Surface?" The Journal of Physical Chemistry C 115(43):21183-21190. DOI: 10.1021/jp205842w

T Lewis, et al. 2011. "Dissociation of Strong Acid Revisited: X-ray Photoelectron Spectroscopy and Molecular Dynamics Simulations of HNO3 in Water." The Journal of Physical Chemistry B 115(30):9445-9451. DOI: 10.1021/jp205510q

Provided by Pacific Northwest National Laboratory (news : web)