 agrees quite well with the orbital
as calculated from theoretical models
(bottom). Each image is 0.6 nanometer by 0.6
nanometer in size. Colors represent the
amplitude of the quantum wave function--the
electron is most likely to be found at the red
and dark blue locations.)
ELECTRON ORBITAL of a nitrogen molecule as
imaged (top) agrees quite well with the orbital
as calculated from theoretical models
(bottom). Each image is 0.6 nanometer by 0.6
nanometer in size. Colors represent the
amplitude of the quantum wave function--the
electron is most likely to be found at the red
and dark blue locations.
Image: DAVID M. VILLENEUVE
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In the quantum world, objects are described by wave functions. Electrons around a molecule, for example, exist in wavelike orbitals, smeared-out shapes that determine properties such as the electrons' energy and the propensity for the molecule to undergo various chemical reactions. But orbitals are slippery critters that, because of Heisenberg's uncertainty principle, defy routine efforts to image them completely and accurately. Now, however, researchers at Canada's National Research Council in Ottawa have produced a three-dimensional scan of the outermost electron orbital around a nitrogen molecule. The "shutter speed" of the imaging method is fast enough that scans might one day be taken of molecules caught in the middle of a chemical reaction.
The group, led by Paul B. Corkum and David M. Villeneuve, uses a laser pulse lasting just 30 femtoseconds (3 x 10¿14 second). During the course of the laser pulse, the electric field of the light wave oscillates about a dozen times. Each oscillation drives the outermost electron of the nitrogen molecule away from the molecule and back again.
Although it might seem that the team relies on a laser to "light up" the electron, it is actually the electron on its way back toward the molecule that acts as the imaging beam. More precisely, the laser's field drives a small proportion of the electron's wave function away and back. Think of it as the electron being in two places at once; mostly it is still in place in its original orbital around the nitrogen, but partly it is being ripped away.
The sharp acceleration turns the traveling electron wave into a plane wave, like a nice regular pulse of an electron beam with an extremely short wavelength--exactly the kind of beam useful for imaging. When the plane wave returns and crosses the molecule, it produces an interference pattern with the stationary part of the electron wave function, like two trains of water waves crossing and forming a checkerboard disturbance.
To complete the imaging, that interference pattern must be detected. As the plane wave travels along, the pattern oscillates rapidly, causing it to emit ultraviolet radiation that the researchers observe. Information about the shadow of the electron orbital as seen by the traveling electron wave is imprinted on the ultraviolet emission. Producing a three-dimensional image requires repeating the process at different angles, like a hospital CT scanner. The angles are set by aligning all the nitrogen molecules in the sample with a somewhat weaker laser pulse a few picoseconds (10¿12 second) before the imaging pulse arrives.
The result of the imaging agrees quite well with the shape of the electron orbital computed theoretically. "I was very excited when I saw the experimentally obtained images of molecular orbitals for the first time," says Ferenc Krausz of the Max Planck Institute of Quantum Optics near Munich. "The technique has great potential." In late 2003 Krausz's group demonstrated another kind of imaging using 250-attosecond (2.5 x 10¿16 second) pulses of extreme ultraviolet light, the shortest light pulses ever produced. The two methods are complementary--Krausz's involving the dynamics of inner electrons, Corkum and Villeneuve's working on the outermost electrons.
Of great interest will be the application of the technique to more complicated molecules and to molecules caught in the process of undergoing a chemical reaction. Villeneuve says he is considering trifluoromethyl iodide, which can be broken up by pulses from the group's laser. "Then we could follow the dissociation," he says, "and measure how the atoms move."
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Reply | Report Abuse | Link to thisToday, 9 March 2012, over CBC radio at about 5:00 AM Pacific time, I heard that an International group of physicists in Regina, Saskatchewan, Canada, under the name of 'Gluex' are searching for evidence of gluon particles. That is why I came searching for the article of April 2005 by Graham P. Collins about ‘CT Scan for Molecules’. The article describes work done by Canada's National Research Council, Ottawa.
The lead researchers were David M. Villeneuve and Paul B. Corkum. Their research was about the electron, whose image you no longer present. It is still in our magazines, and if you magnify the two opposed and magnetically squashed on their inner faces yellow circled red blobs, which are a cut view of the outer valence ring conductor around a nitrogen molecule, it is then likely you will see magnetically compressed cuboidal quarks in a surround of gluons.
For a good description of Cuboidal colloids, see Nature journal, 5 December 2009, 'Soft is strong', p.45 second-last paragraph. In that article and the other article on p.83 in the same issue, where colloids are in discussion, may be a good location to find and understand something about gluons.
While looking at the red blobs, pay particular attention to the above and below, very blurry, induction zones of vibrating, standing magnetic waves. They are two opposed portions of the electron-signature-circle. The other two parts of the ESC are the two opposed hemi-ring capacitors. There are several others of scientist's created images that show the ESC.
If the above is of interest, then e-mail a request to me and I will be happy to lead you to other images of the ESC.
Ed McCarvill
While reading the free samples of 'Astrophysics' and 'Climate Change' in 'Introducing BRIEFINGS', and in order to continue reading, I kept loosing my place in the being read article. That was so as one must continue to raise the page, which moves in jerks, or possibly done two-handed.
Reply | Report Abuse | Link to thisTherefore, if the columns were not vertical, but were instead across the page one would require few shifts, or possibly none for your short but informative articles.
Until then, I shall pass on subscribing. That is, unless they are made in paper-print issue and delivered by mail, Which is no longer done to Canada or to the rest of the non-USA world, from the American Geophysical Union's paper issue of Eos, since Jan.2012.
Perhaps Scientific American could take up the slack by printing the Eos weekly issues and including 4.3 issues each month for an increase in subscription prices. USA is the only country they still post the paper copies to, and send them now in a neat plastic jacket like you guys once did. Those jackets would save us from receiving our issues two to three weeks later than the normal 3to4 weeks after publish date, while later prints some times arrive on schedule and with no jam in between two pages. That non-delivery situation leaves the rest of the world's readers of Eos as second class citizens. Scientists state, "THERE ARE NO BOUNDERIES TO SCIENCE" That no longer applies, as there are now "no delivery zones" outside of USA zones for American Geophysical Union's Eos weekly paper.
I could take my portable, non-electric, paper copy with me were ever I go, and have no worry about it being stolen as would occur possibly with my lap-top or other classifications of readers, of which I know nothing about in this my 77th. year.
Ed McCarvill