Watching electrons in molecules

Oct 14, 2011
The picture shows the conical intersection and the two possible electronic states of the NO2 molecule before it dissociates. (Wörner /ETH Zürich)

(PhysOrg.com) -- 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 for his studies of using ultrashort . 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 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 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 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 . 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 : "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 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 and making artificial photosynthesis possible.

Explore further: The unifying framework of symmetry reveals properties of a broad range of physical systems

More information: H. J. Wörner et al., Conical Intersection Dynamics in NO2 Probed by Homodyne High-Harmonic Spectroscopy. Science, doi:10.1126/science.1208664

Related Stories

Scientists track electrons in molecules

Jun 13, 2010

(PhysOrg.com) -- Physicists in Europe have successfully glimpsed the motion of electrons in molecules. The results are a major boon for the research world. Knowing how electrons move within molecules will ...

Watching Electrons with Lasers

Nov 06, 2008

(PhysOrg.com) -- A team of researchers from the Stanford PULSE Institute for Ultrafast Energy Science at SLAC National Accelerator Laboratory has recently moved a step closer to visualizing the motions of ...

Physicists observe electron ejected from atom for first time

Oct 12, 2010

Physicists at the University of California, Berkeley in collaboration with researchers from the Max Planck Institute of Quantum Optics and the U.S. Department of Energy's Lawrence Berkeley National Laboratory, became the ...

Scientists make holograms of atoms using electrons

Jan 06, 2011

(PhysOrg.com) -- While holography is often associated with artistic 3D images, it can also be used for many other purposes. In a new study, scientists have created holograms of atoms using laser-driven electron ...

Recommended for you

What time is it in the universe?

10 hours ago

Flavor Flav knows what time it is. At least he does for Flavor Flav. Even with all his moving and accelerating, with the planet, the solar system, getting on planes, taking elevators, and perhaps even some ...

Watching the structure of glass under pressure

Aug 28, 2014

Glass has many applications that call for different properties, such as resistance to thermal shock or to chemically harsh environments. Glassmakers commonly use additives such as boron oxide to tweak these ...

Inter-dependent networks stress test

Aug 28, 2014

Energy production systems are good examples of complex systems. Their infrastructure equipment requires ancillary sub-systems structured like a network—including water for cooling, transport to supply fuel, and ICT systems ...

Explainer: How does our sun shine?

Aug 28, 2014

What makes our sun shine has been a mystery for most of human history. Given our sun is a star and stars are suns, explaining the source of the sun's energy would help us understand why stars shine. ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

resinoth
5 / 5 (1) Oct 14, 2011
a video of the data would be great