Atomic Orbitals Imaged

joshv writes "Ever think that physics professor was smokin dope as he described those mysteriously shaped clouds of electron probability floating around atoms? Here's proof. Someone has managed to image atomic orbitals using X-ray crsytallography." The story's from Scientific American; very cool stuff. This may be old hat to physics grads, but it's interesting to us laypeople. ;-)

Comments

Re:Funny...

[Masem]

...And then if you talk to chemists, they'll say physics is a specialization of chemistry :-).

To be truthful, probably 99% of the physists out there are either doing the work at the quantum level (and thus can be called physical chemists), or work at the extreme macroscale (that is, universal scale), and thus can be called astrophysists.

Almost everything in between was solved by Newton way back when, and Einstein in the early part of this century, except for the connection between a 'small' number of molecules (on the order of 1 to 10^10) and the quautum theory level. And that's the job of chemistry :-)

Re:The article doesn't inspire confidence...

[Masem]

Coming from the academica background, my understanding is that the findings in this article, while published in SciAm, are from an article in either Science or Nature. Both of these journal are not generally available to the public, although, most university libraries will carry them. The common form of articles that go into these journal are generally the first major breakthrough findings on some topic; the reported results are sufficient to back up the writers' theories and postulates, but are usually not enough to build a full picture of what's going on.

Thus, I suspect that the details in this SciAm are about as deep as they are in the Nature or Science article, just rewritten to a slightly lower reader level (not too low, mind you, just low enough for the scientific layman to understand). Yes, you should expect contriversy about it. If I remember correctly, the Cold Fusion project of years back underwent a similar treatment. And if you look at the Nobel prizes in Chemistry or Physics and note where the first reported mention of the work occured, I'd expect that you'd also find contrivesry as the idea was tossed around the scientific community.

Now, there is one last point: both Science and Nature are what are known as peer-reviewed journals: before you can publish in those, your article is subjected to critism from at least 3 experts in the field (these experts are anonymous). If they find something fishy or questionable, they'll ask you to fix it , or not approve the article for publication. The fact that it DID get published means that at least 3 experts agree with the results and how the researchers got to them. However, another cavaet - from a chemistry standpoint, this result makes me want to shout horray, as it proves something that's only been shown to work in theory. It's rather easy to ignore possible problems in the mechanics of the experiment for a result like this.

However, now that the technique is out there and reported, you'll see others trying to repeat this, and within 6 months, we'll know if we have the next cold fusion, or the next Nobel-prize winning award.

The article doesn't inspire confidence...

[teraflop user]

X-rays (in crystallography experiments) are not scattered by nuclei, they are scattered by the electron density in the crystal, just like the electron beams. If you want to image nuclei, you have to go to neutron scattering.

The X-ray and electron beams are not combined, they are collected separately, and the information is combined.

Moreover, the principle difficulty has been completely ignored. Electron beams can be focused to produce a direct image. X-rays cannot be focused for imaging purposes (although crude focussing to concentrate a beam is just possible). As a result, you only get a diffraction pattern with no phase information. The image must be reconstructed by Fourier transformation, which needs the phases. (There is a strong analogy with optical holography, in which a reference beam must be interfered with the diffracted beam to obtain phase information, but with x-rays the coherence length is too short to get a reference beam).

The trick is to use the phases from the low resolution electron image, and some mathematical relationships to reconstruct the missing phases in the high resolution image, which will show your electron orbitals. The problem is unless the statistics are treated very carefully, all you get is an image which confirms the assumtions of the model you used to get the relationships with which you reconstruct the phases.

The mathematical techniques were just coming on line in X-ray crystallography in 1996 and there was still considerable debate back then over their correct application. So there is a fair possibility that these results are correct, but I would suspend judgement until they have been scrutinised for a year or two.

Atoms in Molecules (AIM)

[mvw]

I was excited recently to learn that there exists a (more) rigorous derivation of the empirical chemical wisdom that molecules can be described fairly good by considering them built from smaller components (functional groups and atoms of course).

That such a treatment is possible, is not obvious, nature could have been that way, that one had to treat the whole system (like solving the wave equation for all particles at once) in order to make any useful statement at all.

Read this article on Atoms in Molecules by Richard Bader to find out more.

Bader claims that the study of the Laplacian (2nd spatial derivative) of the electron distribution leads to a natural spatial decomposition of a molecule.

Have a look at these great pictures for some simulations based on that AIM theory.

I am still surprised, that during my physics studies, I heard nothing about that treatment. You get exposed to Feynman of course, but Schwinger's formulation of quantumn electro dynamics I knew only as possible but not practical alternative. Very interesting to see Schwingers approach at the heart of this AIM theory.

Philosophical Questions Still Not Resolved

[TheBeginner]

As the article states, electron orbital clouds have long been used to explain chemical reactions mathematically. Now, it says, they have a physical application as well. However (while not a physics major) I believe the key philisophical question is still unanswered. For those of us who do not believe in any sort of God (or do not feel the idea of God is necessary), materialists, the question we are left with is what governs our everyday activity. Is there free will? Is everything cause and effect? With enough understanding can we eventually be able to determine everyone's future?

The answer for me has always been found in Heisenberg's (sp?) uncertainty principle. He states that you can never know the velocity and the position of an electron at the same moment. What this means to me is that no matter how deep or how complete our physical understanding is, there will always be some bit of uncertainty, if only on the minutest level, that allows us to operate as if we had free will. To me, free will is necessary for me to view my life as a worthwhile pursuit.

Thus, while we can now picture the movements of electrons physically, in doing so, we disturb their velocity and Heisenburg's uncertainty principle is still valid. Therefore, while this may have increased our understanding of the universe, it has not destroyed what I feel is the basic necessity for the pursuit of life: free will.