Field of Science

First pentacene, now this

It just seems to get better. Last week a stellar AFM picture of pentacene showing the molecules with unprecedented resolution made the news. This week the picture seems to get even deeper

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The pictures, soon to be published in the journal Physical Review B, show the detailed images of a single carbon atom's electron cloud, taken by Ukrainian researchers at the Kharkov Institute for Physics and Technology in Kharkov, Ukraine.

This is the first time scientists have been able to see an atom's internal structure directly. Since the early 1980s, researchers have been able to map out a material's atomic structure in a mathematical sense, using imaging techniques.

Quantum mechanics states that an electron doesn't exist as a single point, but spreads around the nucleus in a cloud known as an orbital. The soft blue spheres and split clouds seen in the images show two arrangements of the electrons in their orbitals in a carbon atom. The structures verify illustrations seen in thousands of chemistry books because they match established quantum mechanical predictions.

David Goldhaber-Gordon, a physics professor at Stanford University in California, called the research remarkable.

"One of the advantages [of this technique] is that it's visceral," he said. "As humans we're used to looking at images in real space, like photographs, and we can internalize things in real space more easily and quickly, especially people who are less deep in the physics."

To create these images, the researchers used a field-emission electron microscope, or FEEM. They placed a rigid chain of carbon atoms, just tens of atoms long, in a vacuum chamber and streamed 425 volts through the sample. The atom at the tip of the chain emitted electrons onto a surrounding phosphor screen, rendering an image of the electron cloud around the nucleus.
Whenever I see something like this I always wonder how utterly exhilarated and astonished Dalton, Boltzmann, Maxwell, Heisenberg, Bohr, Einstein and others would have been if they had seen all this. I remember that Stuart Schreiber's life trajectory was set when he saw orbitals first presented as gorgeous lobes in class. The Schreibers of the twenty-first century could have much more to be excited about. Man's dominion over the understanding and manipulation of matter sometimes seems almost mythical.

Update: After thinking about this a little more and looking at the comment in the comment section my exhilartion has been tempered by skepticism (for a good scientist it should ideally be the other way around...I am still learning). The orbitals look perfect, and I would be interested in knowing what kind of actual techniques they use to process the initial raw data into this finished image. Plus, what about sp3 hybridization?


  1. Why the S orbital in one case and the P orbital in another. Shouldn't we be seeing both? The second picture appears to be an unhybridized P orbital. Where are the other two?

    What about hybridization? Shouldn't we be seeing four sp3 orbitals?

    It seems a bit too pat

    Note that the presence of a node in the P orbital means that there is zero chance of finding the electron there. This brings up the question of how the electron gets from one lobe to the other. This was brought up in QM class by the prof.

    He says that there are 3 responses to "what does it mean" the first being wrong, the second 2 totally unsatisfying.

    l. Einstein -- hidden variable -- proved wrong by Aspect showing experimental results violate Bell's theorem -- he hopes to get to this later on in the class

    2. Bohr -- the electron isn't anywhere until you measure it

    3. Don't ask

    Clearly (to me at least) the presence of nodes means you have to give up the notion of an electron trajectory.


  2. Good questions, all. Now I am more skeptical. As for the "pure" orbitals in the picture, I wonder if they just extracted them from a combination. As for the node, does QM say there is *zero* probability of finding it there? I would think it's like tunneling and there's probably some non-zero probability. The Aspect experiments and Bell's theorem did indeed challenge Einstein. The final word of course belongs to Feynman who pithily noted that "I think it's safe to say that nobody understand quantum mechanics"

  3. Have a look at linked article from the same group. Figure 3 and 5 are especially interesting.

  4. Wasn't there a great deal of buzz over similar claims in the late 1990s of someone "observing" orbitals in copper atoms, if I remember correctly?

    Orbitals are mathematical constructs used to approximate the electronic structure of multi-electron atoms based on similarities to the hydrogen atom (for which the s, p, etc. orbitals are "exact", at least in non-relativistic QM). I don't think you can really observe orbitals. Electron densities are certainly real and observable, but I don't see how you could claim to observe electron densities arising from individual orbitals. Eric Scerri (UCLA) wrote a great deal about the 1990s claim of observing orbitals. I often don't agree with Scerri's assessment of things, but his criticisms of those previous claims seemed sound (again, if I remember correctly).

  5. I agree with you. An orbital is most accurately defined as a single electron wavefunction, and thus an unobservable construct. I also don't understand how you can isolate and observe single orbitals. I guess we will have to read and try to understand the paper.

  6. I'm very skeptical over this. As you have both pointed out first, how is it possible to isolate single orbitals? how do you take their "picture" without interacting(tempering) with them (remembering Heisenberg)?
    As for hybridization, I think this is the least of our concerns since it is not existent. Remember that Pauling's great contribution was to adapt, by symmetry, a bunch of functions which were not a basis in the Td point group to another bunch of functions which were, by making use of the fact that any linear combination of Hamiltonian's eigenfunctions would also be one.
    I wrote a little something about this some months ago in:

    As for what Swheele2 says, I remember it too. It appeared in Nature (or was it Science?) around the year 2001. I was told that the authors retracted some years later but I didn't follow the story.

    I like your blog a lot, too bad I don't have too much time to read all I like on the web. Keep it up!


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