Complete Measurement of Molecular Breakup 32
Suidae writes "PhysicsWeb is reporting that physicists have made a 'complete' measurement of the break-up of a molecule for the first time. Reinhard Dörner of the University of Frankfurt and co-workers in Germany, the US, Australia and Spain recorded the two electrons and two nuclei that were released when a single photon split a molecule of deuterium into its basic components. The experiment could lead to a better understanding of many physical and chemical processes through improved knowledge of the quantum dynamics of many-particle systems."
Confusing (Score:1, Informative)
FP BTW.
Re:Confusing (Score:1, Interesting)
Even weirder is this statement:
Excuse me? A deuterium nucleus has a proton and a neutron... only one of these has a positive charge.
Re:Confusing (Score:1)
Re:Confusing (Score:4, Informative)
75 eV isn't nearly enough to split the nucleus apart anyways.
I wonder why they used deuterium molecules rather than just hydrogen, though. I understand why they used hydrogen -- a hydrogen-hydrogen molecule is the simplest possible molecule -- but why deuterium?
Let me see if I can answer my own question ...
Deuterium has somewhat different chemical properties than hydrogen due to the different nuclear mass (classically, it's a two body problem, look up `reduced mass' if you want more details.) With a larger nucleus mass, the electrons would have a lower average kinetic energy, and by the virial theorem the average potential energy would therefore be higher (KE = - 1/2 PE) (a smaller absolute value, but it's negative, so it's higher) and therefore less tightly bound.
So, I'm guessing they used deuterium molecules instead of hydrogen molecules because it would require less energy to split them apart. They're making things as easy as possible ...
Re:Confusing (Score:2)
I missed this part earlier. I guess I should read more carefully before I try to figure stuff out on my own :)
As they say -- a couple of months in the laboratory can frequently save a couple of hours in the library. :)
I'm not sure their explanation really makes sense, however. It may just be overly simplified for the press ...
Re:Confusing (Score:1)
But that's not what they want to do. As someone must have (I mean, am I the only person who remembers high school chemistry?) mentioned it already, they are splitting an H_2 molecule into two atoms of H. (At the end, H- ions, presumably.) The fact that they are using deuterium doesn't change anything except that the H- ion is twice as heavy and that the target area (er, "cross-section," is probably the correct term).
BTW, where did you get th
Re:Confusing (Score:1)
Re:Confusing (Score:5, Informative)
You seem to be confusing the meaning of 'nuclei' with 'subatomic particle'. Nuclei is the plural form of nucleus. They're talking about two seperate "nucleuses" which are flying apart, because both have an overall positive charge thanks to the proton, so both repel each other.
To clarify what actually happened here: They started with a single molecule of deuterium. A molecule of deuterium is simply two deuterium atoms (deuterium is just like hydrogen, only it has a neutron in the nucleus as well) in a covalent bond, the exact same way hydrogen is normally found as an H2 molecule.
Then they shot a photon at their molecule, which knocked the two electrons being shared by the two atoms away. Since the sharing of electrons is what causes a covalent bond to be happen in the first place, the bond breaks up, and they measure exactly what happened.
Re:Confusing (Score:1)
What I was pointing out is that the article *did not make sense* as written. That is all.
Re:Confusing (Score:2, Insightful)
Re:Confusing (Score:1)
I can't figure out *what* I was thinking earlier. I must be suffering from a lack of caffeine or something. I'm going to go remedy that right now.
Thank you for being a witness to my idiocy.
Confused by your confusion (Score:3, Insightful)
A photon is used to break apart a molecule. Measurments are made; stuff might be learnt.
It's actually a pretty good summary, especally by
Re:Confused by your confusion (Score:2)
How does this stuff get modded up? (Score:3, Informative)
That's like saying the iMac is an Apple, not a computer. Yes, Deuterium is an isotope of hydrogen. That does not preclude Deuterium molecules. Actually, it predicts it. We get D2 just like we get H2. But if you want to get that FP (and first mod) you can't let the facts get in the way.
How is that 'interesting'???? Again, while technically true, that stateme
Re:Confusing (Score:4, Informative)
However, hydrogen (and deuterium, which is just hydrogen with an extra neutron) atoms are almost never found alone. They're found in molecules of two hydrogen atoms. I think that's what they're talking about breaking up.
Re:Confusing (Score:2)
Re:Confusing (Score:2)
Re:Confusing (Score:1, Insightful)
If the neutron had been converted into an electron and a proton like you imply above, we would have been talking about a subnuclear reaction or something and it would have taken a lot more than 75.5 eV.
Re:Confusing (Score:5, Informative)
It's sometimes hard for people to bear in mind, but isotopes actually DO behave almost identically to each other in most non-nuclear chemical reactions.
I found it very interesting when I was doing NMR (nuclear magnetic resonance; used to help determine molecular structures) work in the labs, we had to use deuterated solvents, so that they would resonate differently and therefore could be removed from the resulting data. Therefore, I would use D2O (deuterated water) and other common solvents that had all the hydrogens replaced with deuterium. Aside from the very expensive pricetag, you'd never have known the difference.
Re:Confusing (Score:2)
Deuterium poisoning. (Score:5, Informative)
This is because the chemical behaviors of deuterium and light hydrogen are slightly different.
You can think of the electron and nucleus co-orbiting about a common centre of mass, rather than the electron orbiting while the nucleus remains fixed. Where the point is depends on the ratio of the masses of the electron and the nucleus (about 2000:1 for light hydrogen, and about 4000:1 for deuterium). The different orbit radius (for any given energy) for each case means that the energy level at which the orbit circumference is an integer number of electron wavelengths will be different for deuterium and light hydrogen.
This means that the energy structure of the electron shells is slightly different, which means that they will behave slightly differently chemically. This fact is exploited in some of the methods of isolating heavy hydrogen from light hydrogen (electrolysis method, as the reduction potential is different, and the more common chemical method involving forming hydrogen sulphide, as the rates of reaction are different).
In the case of ingestion, deuterium's chemical behavior is similar enough to that of hydrogen that it gets incorporated into chemicals and otherwise interacted with as hydrogen would be, but different enough that it mucks up some of these reactions. Result, poisoning, much as you get from heavy metals displacing their chemical analogues (though less so, because D and H are a lot more similar, and your body cycles hydrogen through itself pretty quickly, while metals tend to accumulate).
As far as hydrogen isotopes go, though, tritium is the main concern. It's a beta emitter, and is formed in water-cooled reactors (especially the heavy-water-moderated reactors Canada uses, as only one transmutation step is required instead of two). It's a very low-energy emitter, but if ingested, will still cause problems. It's less nasty than most contaminents, though, as hydrogen gets cycled through the body very quickly, and tritium has a half-life of about a decade (short enough to disappear within a lifetime, long enough that it cycles out of the body without depositing much of its radiation dose).
Deuterium is mildly chemically toxic, but is not radioactive.
Dr. Phil.. (Score:1)
Now do you believe I RTFA?
So... how is this significant at all? (Score:2, Interesting)
Hydrogen atom (thus, I think, molecules...) is very well-studied theoretically. Gosh, they don't just stop at calculating different energy levels due to Coulomb force. At third-year level of undergraduate physics classes, they already calculate fine-structure splitting, hyperfine splitting, and even Zeeman splitting, in presense of a magnetic field. At that level, t
Re:So... how is this significant at all? (Score:2)
Singly-ionized hydrogen is simpler but isn't stable.
Re:So... how is this significant at all? (Score:1)
which is pretty close to true at normal energies,
visible light, for instance. Pumping the energy up into this range gets to the point where you can't ignore the nuclear motion, so you get into areas where the usual equations don't work. Having real measurements of what is going on helps
Re:So... how is this significant at all? (Score:1)
I see... come to think of it, energy corresponding to 70+ eV is almost half-an-order-of-magnitude larger than the ionization energy of hydrogen. But, in case of H_2, is it really that much of a many-body problem? (I mean, I do understand that it is a four-body problem, but that's not nearly as complicated as solar system...)
Well, on the second tho
Re:So... how is this significant at all? (Score:1)