Complete Measurement of Molecular Breakup

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."

Comments

Re:Confusing

[wjwlsn]

Even weirder is this statement:

In the experiments a single photon has enough energy (75.5 electron volts) to knock both electrons out of a deuterium molecule, and the two nuclei then fly apart because they are both positively charged.

Excuse me? A deuterium nucleus has a proton and a neutron... only one of these has a positive charge.

So... how is this significant at all?

[novakyu]

Not to play down the importance of experiments in physics (gosh, I'm a physicist. I should know), but how is this experiment important at all?

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, the theory is getting so accurate, and the energy level splitting becomes so small that if you want to fit a photon of right energy between the energy levels, you have to go down to the frequency of radio waves. It's not like we need experimental results (as in the case of more complicated atoms) because you can't solve (or approximate very closely) for the energy levels of the atom.

Since deuterium is practically identical to hydrogen, unless you want to study the nucleus itself (I mean... it's two fermions, so something must be different, even though they are not identical particles), what's the point of publishing results of an experiment like this? This sounds not much more sophisticated (or important) than the experiments done in advanced physics lab (er... optical pumping, Rutherford scattering, NMR, etc. etc.).

It would be a totally different matter if they found something that contradicted predictions of an established theory...but, did they?