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article imageScientists capture first-ever image of atoms moving in a molecule

By JohnThomas Didymus     Mar 8, 2012 in Science
Scientists at Ohio and Kansas State Universities say they have captured the first-ever image of atoms moving in a molecule. They used a laser to knock an electron out of its orbit and used the diffraction pattern to construct a 3D "movie" of the atom.
When ultra-fast laser pulses hit the target atom of the molecule at the moment the atom is bonding with another to form the molecule, it knocks an electron out of its orbit, but when the electron falls back to its orbit, it emits an energy signal that, like a ripple in a pond, can be detected. According to Science Daily, the recorded signals from a single electron in the interval between ultra-fast laser pulses(one quadrillionth of a second) are used as "flash bulb" signals to record the changes as the molecule is formed through bond formation between atoms. The changes in the molecule are recorded in the image generated, using a color code scale of dark blue to pink, as increase in angular momentum. Pink stands for regions of greatest momentum while dark blue stands for regions of lowest momentum.
According to News Wise, the technique is called Laser Induced Electron Diffraction (LIED) and is commonly used in surface science to study solid materials, but this is the first time LIED has been used to study a single molecule as it is formed.
The scientists used simple molecules for their study. They caused two nitrogen (N) atoms to bond together and form molecular nitrogen (N2).They repeated the experiment using two oxygen atoms to form molecular oxygen (O2). Using these two common atmospheric gases with molecule formation mechanisms that are very well known allows scientists to test the accuracy of the LIED technique.
In the experiment, energy released as the electron falls back into the molecule generates a diffraction pattern that is used to construct a 3D image of the molecule, which includes the size, shape of the molecule and location of the constituent atom's nuclei and the electron shells orbiting it.
Popular Science observes that the very short time interval (50 femtoseconds or a quadrillionth of a second) between laser pulses makes it possible to capture the change in the atoms within a short time, allowing a frame-by-frame "movie" of atomic motion within the forming molecule.
The researchers say the 3D image generated was the first image ever recorded of bonds forming in a molecule.
According to principal investigator Louis DiMauro, professor of physics at Ohio State University, the latest achievement is a major step towards learning to control reaction mechanisms at the atomic scale. Beside its potential use for controlling chemical reactions, LIED may also provide new tools for observing what goes on during formation of molecular bonds, and give insight into the structure and dynamics of matter. Blaga said: "Ultimately, we want to really understand how chemical reactions take place. So, long-term, there would be applications in materials science and even chemical manufacture. You could use this to study individual atoms, but it's safe to say that we won't learn anything new from an atomic physics standpoint. The greater impact to science will come when we can study reactions between more complex molecules. Looking at two atoms -- that's a long way from studying a more interesting molecule like a protein."
DiMauro said: "Through these experiments, we realized that we can control the trajectory of the electron when it comes back to the molecule, by adjusting the orientation of the laser that launches it. The next step will be to see if we can hit the electron in just the right way to actually control a chemical reaction."
News Wise reports that a more commonly used technique involves bombarding the molecule with millions of electrons per second. But, according to the researchers, the new LIED method that involves shooting only one electron at the molecule is more reliable and yields more accurate results.
Co-author of the paper, Ohio postdoctoral researcher Cosmin Blaga, said: "If we shot an electron beam from outside the molecule, there would only be a certain probability that one of the electrons would scatter off the molecule. But in this case, when we use a laser to launch an electron from inside the molecule we are studying, we have a 100 percent probability that it will fall back into the molecule and scatter."
News Wise reports co-authors of the study include Anthony DiChiara, Emily Sistrunk, Kaikai Zhang, Pierre Agostini, Terry A. Miller of Ohio State, and C.D. Lin of Kansas State.
More about Atoms, molecules, Lied, Diffraction, first ever image of atoms
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