Watching motion of electrons in molecules during chemical reactions

ScienceDaily (Oct. 14, 2011) — A research group led by ETH Zurich has now, for the first time, visualized the motion of electrons during a chemical reaction. The new findings in the experiment are of fundamental importance for photochemistry and could also assist the design of more efficient solar cells.

In 1999, Ahmed Zewail was awarded the nobel prize in chemistry for his studies of chemical reactions using ultrashort laser pulses. Zewail was able to watch the motion of atoms and thus visualize transition states on the molecular level. Watching the dynamics of single electrons was still considered a dream at that time. Thanks to the latest developments in laser technology and intense research in the field of attosecond spectroscopy (1 attosecond = 10-18 s) the research has developed fast. For the first time, Prof. Hans Jakob Wörner from the Laboratory of Physical Chemistry at ETH Zurich, together with colleagues from Canada and France, was able to record electronic motion during a complete chemical reaction. The experiment is described in the latest issue of Science.

The research team irradiated nitrogen dioxide molecules (NO2) with a very short ultraviolet pulse. Subsequently, the molecule takes up the energy from the pulse which sets the electrons in motion. The electrons start rearranging themselves, which causes the electron cloud to oscillate between two different shapes for a very short time, before the molecule starts to vibrate and eventually decomposes into nitric oxide and an oxygen atom.

Conical intersections

Nitrogen dioxide has model character with respect to understanding electronic motion. In the NO2 molecule, two states of the electrons can have the same energy for a particular geometry -- commonly described as conical intersection. The conical intersection is very important for photochemistry and frequently occurs in natural chemical processes induced by light. The conical intersection works like a dip-switch. For example, if the retina of a human eye is irradiated by light, the electrons start moving, and the molecules of the retina (retinal) change their shape, which finally converts the information of light to electrical information for the human brain. The special aspect about conical intersections is that the motion of electrons is transferred to a motion of the atoms very efficiently.

Snapshot of an electron

In an earlier article, Hans Jakob Wörner has already published how attosecond spectroscopy can be used for watching the motion of electrons. The first weak ultraviolet pulse sets the electrons in motion. The second strong infrared pulse then removes an electron from the molecule, accelerates it and drives it back to the molecule. As a result, an attosecond light pulse is emitted, which carries a snapshot of the electron distribution in the molecule. Wörner illustrates the principle of attosecond spectroscopy: "The experiment can be compared to photographs, which, for example, image a bullet shot through an apple. The bullet would be too fast for the shutter of a camera, resulting in a blurred image. Therefore, the shutter is left open and the picture is illuminated with light flashes, which are faster than the bullet. That's how we get our snap-shot."

From the experiment to solar cells

When the electron returns to the molecule, it releases energy in the form of light. In the experiment, Wörner and his colleagues measured the light of the electrons and were therefore able to deduce detailed information on the electron distribution and its evolution with time. This information reveals details of chemical reaction mechanisms that were not accessible to most of previous experimental techniques. The experiment on NO2 helps understanding fundamental processes in molecules and is an ideal extension of computer simulations of photochemical processes: "What makes our experiment so important is that it verifies theoretical models," says Wörner. The immense interest in photochemical processes is not surprising, as this area of research aims at improving solar cells and making artificial photosynthesis possible.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by ETH Zürich.

Journal Reference:

H. J. Worner, J. B. Bertrand, B. Fabre, J. Higuet, H. Ruf, A. Dubrouil, S. Patchkovskii, M. Spanner, Y. Mairesse, V. Blanchet, E. Mevel, E. Constant, P. B. Corkum, D. M. Villeneuve. Conical Intersection Dynamics in NO2 Probed by Homodyne High-Harmonic Spectroscopy. Science, 2011; 334 (6053): 208 DOI: 10.1126/science.1208664

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Watching motion of electrons in molecules during chemical reactions

ScienceDaily (Oct. 14, 2011) — A research group led by ETH Zurich has now, for the first time, visualized the motion of electrons during a chemical reaction. The new findings in the experiment are of fundamental importance for photochemistry and could also assist the design of more efficient solar cells.

In 1999, Ahmed Zewail was awarded the nobel prize in chemistry for his studies of chemical reactions using ultrashort laser pulses. Zewail was able to watch the motion of atoms and thus visualize transition states on the molecular level. Watching the dynamics of single electrons was still considered a dream at that time. Thanks to the latest developments in laser technology and intense research in the field of attosecond spectroscopy (1 attosecond = 10-18 s) the research has developed fast. For the first time, Prof. Hans Jakob Wörner from the Laboratory of Physical Chemistry at ETH Zurich, together with colleagues from Canada and France, was able to record electronic motion during a complete chemical reaction. The experiment is described in the latest issue of Science.

The research team irradiated nitrogen dioxide molecules (NO2) with a very short ultraviolet pulse. Subsequently, the molecule takes up the energy from the pulse which sets the electrons in motion. The electrons start rearranging themselves, which causes the electron cloud to oscillate between two different shapes for a very short time, before the molecule starts to vibrate and eventually decomposes into nitric oxide and an oxygen atom.

Conical intersections

Nitrogen dioxide has model character with respect to understanding electronic motion. In the NO2 molecule, two states of the electrons can have the same energy for a particular geometry -- commonly described as conical intersection. The conical intersection is very important for photochemistry and frequently occurs in natural chemical processes induced by light. The conical intersection works like a dip-switch. For example, if the retina of a human eye is irradiated by light, the electrons start moving, and the molecules of the retina (retinal) change their shape, which finally converts the information of light to electrical information for the human brain. The special aspect about conical intersections is that the motion of electrons is transferred to a motion of the atoms very efficiently.

Snapshot of an electron

In an earlier article, Hans Jakob Wörner has already published how attosecond spectroscopy can be used for watching the motion of electrons. The first weak ultraviolet pulse sets the electrons in motion. The second strong infrared pulse then removes an electron from the molecule, accelerates it and drives it back to the molecule. As a result, an attosecond light pulse is emitted, which carries a snapshot of the electron distribution in the molecule. Wörner illustrates the principle of attosecond spectroscopy: "The experiment can be compared to photographs, which, for example, image a bullet shot through an apple. The bullet would be too fast for the shutter of a camera, resulting in a blurred image. Therefore, the shutter is left open and the picture is illuminated with light flashes, which are faster than the bullet. That's how we get our snap-shot."

From the experiment to solar cells

When the electron returns to the molecule, it releases energy in the form of light. In the experiment, Wörner and his colleagues measured the light of the electrons and were therefore able to deduce detailed information on the electron distribution and its evolution with time. This information reveals details of chemical reaction mechanisms that were not accessible to most of previous experimental techniques. The experiment on NO2 helps understanding fundamental processes in molecules and is an ideal extension of computer simulations of photochemical processes: "What makes our experiment so important is that it verifies theoretical models," says Wörner. The immense interest in photochemical processes is not surprising, as this area of research aims at improving solar cells and making artificial photosynthesis possible.

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by ETH Zürich.

Journal Reference:

H. J. Worner, J. B. Bertrand, B. Fabre, J. Higuet, H. Ruf, A. Dubrouil, S. Patchkovskii, M. Spanner, Y. Mairesse, V. Blanchet, E. Mevel, E. Constant, P. B. Corkum, D. M. Villeneuve. Conical Intersection Dynamics in NO2 Probed by Homodyne High-Harmonic Spectroscopy. Science, 2011; 334 (6053): 208 DOI: 10.1126/science.1208664

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Catalyst discovery potential has to revolutionize chemical industry

ScienceDaily (Sep. 27, 2011) — University of Alberta Chemistry Professor Steve Bergens and his graduate student Jeremy Johns have discovered a catalyst that has the potential to revolutionise the chemical industry by reducing its environmental footprint, improving efficiency and minimizing risks.

Their findings were published in a top international chemistry journal Angewandte Chemie this month and provide the chemical industry with a potential solution to issues surrounding economics, efficiency and environmental factors.

"Our findings are a game changer that people having been seeking an answer to for decades," said Bergens.

Bergen said researchers have been working for more than 50 years to find a "clean" and stable catalyst that produces little to no waste and also has a capacity to provide multiple turnovers. In February of this year his student Jeremy Johns created such a catalyst in his laboratory.

"After years of producing disappointing results I was thrilled to see the results that came out of this particular experiment," said Dr Bergens.

"The chemical industry is making huge efforts to reduce its environmental footprint and their economists and accountants are also looking to reduce the cost of not just transporting catalyst but improving its efficiency," said Dr Bergens.

He said the February 2011 discovery opens numerous doors to make these things happen for industries ranging from pharmaceuticals to agrochemicals.

"Catalysts are notoriously unstable and challenging to transport, and the waste products the reactions to produce chemicals produce are equally challenging," Bergens added.

John's catalyst only produces hydrogen as a waste, something that is easy to burn off or react to produce water.

Bergens says early indications are the catalyst is not just safe but also efficient. The researchers have pushed the experiment to produce 7000 turnovers for one unit of catalyst.

"We are hugely excited , and the challenge now is to identify exactly how this catalyst is made up and how we can produce it in amounts to further advance this discovery," said Bergens.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Alberta, via EurekAlert!, a service of AAAS.

Journal Reference:

Jeremy M. John, Steven H. Bergens. Catalyst for the Hydrogenation of Amides to Alcohols and Amines. Angewandte Chemie International Edition, 2011; DOI: 10.1002/anie.201105348

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Catalyst discovery potential has to revolutionize chemical industry

ScienceDaily (Sep. 27, 2011) — University of Alberta Chemistry Professor Steve Bergens and his graduate student Jeremy Johns have discovered a catalyst that has the potential to revolutionise the chemical industry by reducing its environmental footprint, improving efficiency and minimizing risks.

Their findings were published in a top international chemistry journal Angewandte Chemie this month and provide the chemical industry with a potential solution to issues surrounding economics, efficiency and environmental factors.

"Our findings are a game changer that people having been seeking an answer to for decades," said Bergens.

Bergen said researchers have been working for more than 50 years to find a "clean" and stable catalyst that produces little to no waste and also has a capacity to provide multiple turnovers. In February of this year his student Jeremy Johns created such a catalyst in his laboratory.

"After years of producing disappointing results I was thrilled to see the results that came out of this particular experiment," said Dr Bergens.

"The chemical industry is making huge efforts to reduce its environmental footprint and their economists and accountants are also looking to reduce the cost of not just transporting catalyst but improving its efficiency," said Dr Bergens.

He said the February 2011 discovery opens numerous doors to make these things happen for industries ranging from pharmaceuticals to agrochemicals.

"Catalysts are notoriously unstable and challenging to transport, and the waste products the reactions to produce chemicals produce are equally challenging," Bergens added.

John's catalyst only produces hydrogen as a waste, something that is easy to burn off or react to produce water.

Bergens says early indications are the catalyst is not just safe but also efficient. The researchers have pushed the experiment to produce 7000 turnovers for one unit of catalyst.

"We are hugely excited , and the challenge now is to identify exactly how this catalyst is made up and how we can produce it in amounts to further advance this discovery," said Bergens.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Alberta, via EurekAlert!, a service of AAAS.

Journal Reference:

Jeremy M. John, Steven H. Bergens. Catalyst for the Hydrogenation of Amides to Alcohols and Amines. Angewandte Chemie International Edition, 2011; DOI: 10.1002/anie.201105348

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New driving force for chemical reactions

ScienceDaily (June 9, 2011) — New research just published in the journal Science by a team of chemists at the University of Georgia and colleagues in Germany shows for the first time that a mechanism called tunneling control may drive chemical reactions in directions unexpected from traditional theories.

The finding has the potential to change how scientists understand and devise reactions in everything from materials science to biochemistry.

The discovery was a complete surprise and came following the first successful isolation of a long-elusive molecule called methylhydroxycarbene by the research team. While the team was pleased that it had "trapped" the prized compound in solid argon through an extremely low-temperature experiment, they were surprised when it vanished within a few hours. That prompted UGA theoretical chemistry professor Wesley Allen to conduct large scale, state-of-the-art computations to solve the mystery.

"What we found was that the change was being controlled by a process called quantum mechanical tunneling," said Allen, "and we found that tunneling can supersede the traditional chemical reactivity processes of kinetic and thermodynamic control. We weren't expecting this at all."

What had happened? Clearly, a chemical reaction had taken place, but only inert argon atoms surrounded the compound, and essentially no thermal energy was available to create new molecular arrangements. Moreover, said Allen, "the observed product of the reaction, acetaldehyde, is the least likely outcome among conceivable possibilities."

Other authors of the paper include Professor Peter Schreiner and his group members Hans Peter Reisenauer, David Ley and Dennis Gerbig of the Justus-Liebig University in Giessen, Germany. Graduate student Chia-Hua Wu at UGA undertook the theoretical work with Allen.

Quantum tunneling isn't new. It was first recognized as a physical process decades ago in early studies of radioactivity. In classical mechanics, molecular motions can be understood in terms of particles roaming on a potential energy surface. Energy barriers, visualized as mountain passes on the surface, separate one chemical compound from another.

For a chemical reaction to occur, a molecular system must have enough energy to "get over the top of the hill," or it will come back down and fail to react. In quantum mechanics, particles can get to the other side of the barrier by tunneling through it, a process that seemingly requires imaginary velocities. In chemistry, tunneling is generally understood to provide secondary correction factors for the rates of chemical reactions but not to provide the predominant driving force.

(The strange world of quantum mechanics has been subject to considerable interest and controversy over the last century, and Austrian physicist Erwin Schrödinger's thought-experiment called "Schrödinger's Cat" illustrates how perplexing it is to apply the rules and laws of quantum mechanics to everyday life.)

"We knew that the rate of a reaction can be significantly affected by quantum mechanical tunneling," said Allen. "It becomes especially important at low temperatures and for reactions involving light atoms. What we discovered here is that tunneling can dominate a reaction mechanism sufficiently to redirect the outcome away from traditional kinetic control. Tunneling can cause a reaction that does not have the lowest activation barriers to occur exclusively."

Allen suggests a vivid analogy between the behavior of methylhydroxycarbene and Schrödinger's iconic cat.

"The cat cannot jump out of its box of deadly confinement because the walls are too high, so it conjures a Houdini-like escape by bursting through the thinnest wall," he said.

The fact that new ideas about tunneling came from the isolation of methylhydroxycarbene was the kind of serendipity that runs through the history of science. Schreiner and his team had snagged the elusive compound, and that was reason enough to celebrate, Allen said. But the surprising observation that it vanished within a few hours raised new questions that led to even more interesting scientific discoveries.

"The initiative to doggedly follow up on a 'lucky observation' was the key to success," said Allen. "Thus, a combination of persistent experimentation and exacting theoretical analysis on methylhydroxycarbene and its reactivity led to the concept I dubbed tunneling control, which may be characterized as `a type of nonclassical kinetic control wherein the decisive factor is not the lowest activation barrier'."

While the process was unearthed for the specific case of methylhydroxycarbene at extremely low temperatures, Allen said that tunneling control "can be a general phenomenon, especially if hydrogen transfer is involved, and such processes need not be restricted to cryogenic temperatures."

Allen's research was funded by the U.S. Department of Energy.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Georgia.

Journal Reference:

Peter R. Schreiner, Hans Peter Reisenauer, David Ley, Dennis Gerbig, Chia-Hua Wu, Wesley D. Allen. Methylhydroxycarbene: Tunneling Control of a Chemical Reaction. Science, 10 June 2011: Vol. 332 no. 6035 pp. 1300-1303 DOI: 10.1126/science.1203761

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New driving force for chemical reactions

ScienceDaily (June 9, 2011) — New research just published in the journal Science by a team of chemists at the University of Georgia and colleagues in Germany shows for the first time that a mechanism called tunneling control may drive chemical reactions in directions unexpected from traditional theories.

The finding has the potential to change how scientists understand and devise reactions in everything from materials science to biochemistry.

The discovery was a complete surprise and came following the first successful isolation of a long-elusive molecule called methylhydroxycarbene by the research team. While the team was pleased that it had "trapped" the prized compound in solid argon through an extremely low-temperature experiment, they were surprised when it vanished within a few hours. That prompted UGA theoretical chemistry professor Wesley Allen to conduct large scale, state-of-the-art computations to solve the mystery.

"What we found was that the change was being controlled by a process called quantum mechanical tunneling," said Allen, "and we found that tunneling can supersede the traditional chemical reactivity processes of kinetic and thermodynamic control. We weren't expecting this at all."

What had happened? Clearly, a chemical reaction had taken place, but only inert argon atoms surrounded the compound, and essentially no thermal energy was available to create new molecular arrangements. Moreover, said Allen, "the observed product of the reaction, acetaldehyde, is the least likely outcome among conceivable possibilities."

Other authors of the paper include Professor Peter Schreiner and his group members Hans Peter Reisenauer, David Ley and Dennis Gerbig of the Justus-Liebig University in Giessen, Germany. Graduate student Chia-Hua Wu at UGA undertook the theoretical work with Allen.

Quantum tunneling isn't new. It was first recognized as a physical process decades ago in early studies of radioactivity. In classical mechanics, molecular motions can be understood in terms of particles roaming on a potential energy surface. Energy barriers, visualized as mountain passes on the surface, separate one chemical compound from another.

For a chemical reaction to occur, a molecular system must have enough energy to "get over the top of the hill," or it will come back down and fail to react. In quantum mechanics, particles can get to the other side of the barrier by tunneling through it, a process that seemingly requires imaginary velocities. In chemistry, tunneling is generally understood to provide secondary correction factors for the rates of chemical reactions but not to provide the predominant driving force.

(The strange world of quantum mechanics has been subject to considerable interest and controversy over the last century, and Austrian physicist Erwin Schrödinger's thought-experiment called "Schrödinger's Cat" illustrates how perplexing it is to apply the rules and laws of quantum mechanics to everyday life.)

"We knew that the rate of a reaction can be significantly affected by quantum mechanical tunneling," said Allen. "It becomes especially important at low temperatures and for reactions involving light atoms. What we discovered here is that tunneling can dominate a reaction mechanism sufficiently to redirect the outcome away from traditional kinetic control. Tunneling can cause a reaction that does not have the lowest activation barriers to occur exclusively."

Allen suggests a vivid analogy between the behavior of methylhydroxycarbene and Schrödinger's iconic cat.

"The cat cannot jump out of its box of deadly confinement because the walls are too high, so it conjures a Houdini-like escape by bursting through the thinnest wall," he said.

The fact that new ideas about tunneling came from the isolation of methylhydroxycarbene was the kind of serendipity that runs through the history of science. Schreiner and his team had snagged the elusive compound, and that was reason enough to celebrate, Allen said. But the surprising observation that it vanished within a few hours raised new questions that led to even more interesting scientific discoveries.

"The initiative to doggedly follow up on a 'lucky observation' was the key to success," said Allen. "Thus, a combination of persistent experimentation and exacting theoretical analysis on methylhydroxycarbene and its reactivity led to the concept I dubbed tunneling control, which may be characterized as `a type of nonclassical kinetic control wherein the decisive factor is not the lowest activation barrier'."

While the process was unearthed for the specific case of methylhydroxycarbene at extremely low temperatures, Allen said that tunneling control "can be a general phenomenon, especially if hydrogen transfer is involved, and such processes need not be restricted to cryogenic temperatures."

Allen's research was funded by the U.S. Department of Energy.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Georgia.

Journal Reference:

Peter R. Schreiner, Hans Peter Reisenauer, David Ley, Dennis Gerbig, Chia-Hua Wu, Wesley D. Allen. Methylhydroxycarbene: Tunneling Control of a Chemical Reaction. Science, 10 June 2011: Vol. 332 no. 6035 pp. 1300-1303 DOI: 10.1126/science.1203761

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New material could improve safety for first responders to chemical hazards

ScienceDaily (May 2, 2011) — A new kind of sensor could warn emergency workers when carbon filters in the respirators they wear to avoid inhaling toxic fumes have become dangerously saturated.

In a recent issue of the journal Advanced Materials, a team of researchers from the University of California, San Diego and Tyco Electronics describe how they made the carbon nanostructures and demonstrate their potential use as microsensors for volatile organic compounds.

First responders protect themselves from such vapors, whose composition is often unknown, by breathing through a canister filled with activated charcoal -- a gas mask. Airborne toxins stick to the carbon in the filter, trapping the dangerous materials.

As the filters become saturated, chemicals will begin to pass through. The respirator can then do more harm than good by providing an illusion of safety. But there is no easy way to determine when the filter is spent. Current safety protocols base the timing of filter changes on how long the user has worn the mask.

"The new sensors would provide a more accurate reading of how much material the carbon in the filters has actually absorbed," said team leader Michael Sailor, professor of chemistry and biochemistry and bioengineering at UC San Diego. "Because these carbon nanofibers have the same chemical properties as the activated charcoal used in respirators, they have a similar ability to absorb organic pollutants."

Sailor's team assembled the nanofibers into repeating structures called photonic crystals that reflect specific wavelengths, or colors, of light. The wing scales of the Morpho butterfly, which give the insect its brilliant iridescent coloration, are natural examples of this kind of structure.

The sensors are an iridescent color too, rather than black like ordinary carbon. That color changes when the fibers absorb toxins -- a visible indication of their capacity for absorbing additional chemicals.

The agency that certifies respirators in the U.S., the National Institute of Occupational Safety and Health, has long sought such a sensor but the design requirements for a tiny, sensitive, inexpensive device that requires little power, have proved difficult to meet.

The materials that the team fabricated are very thin -- less than half the width of a human hair. Sailor's group has previously placed similar photonic sensors on the tips of optical fibers less than a millimeter across and shown that they can be inserted into respirator cartridges. And the crystals are sensitive enough to detect chemicals such as toluene at concentrations as low as one part per million.

Ting Gao, a senior researcher at the Polymers, Ceramics, and Technical Services Laboratories of Tyco Electronics in Menlo Park, California and Timothy L. Kelly, a NSERC post-doctoral fellow at UC San Diego co-authored the paper. The National Science Foundation, the Department of Homeland Security, the Natural Sciences and Engineering Research Council of Canada, and TYCO Electronics provided funding for the work.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - San Diego. The original article was written by Susan Brown.

Journal Reference:

Timothy L. Kelly, Ting Gao, Michael J. Sailor. Carbon Nanofiber Photonic Crystals: Carbon and Carbon/Silicon Composites Templated in Rugate Filters for the Adsorption and Detection of Organic Vapors (Adv. Mater. 15/2011). Advanced Materials, 2011; 23 (15): 1688 DOI: 10.1002/adma.201190052

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here