This happens because interactions between molecules in the sample and in the solvent produce common orbitals. The excited electrons are pushed into these orbitals. "This works because the molecular orbitals of the iron and water ions come very close spatially and their energies match very well," explains Emad Aziz, head of a junior research group at HZB. The electrons remain in this new state longer than they would in a normal molecular orbital. Their energy state therefore prevents the emission of the normally expected fluorescent light.
Dips in the spectrum thus give a clue as to the kind of interplay between the sample and the solvent. One could use this process to examine how much the solvent contributes towards the function of biochemical systems such as pro-teins, for example.
Ultrafast processes such as charge transfer have only been observable with enormous effort using conventional methods. Now, HZB researchers have found a way to explain the dynamics of this process using a simple model. "We can observe where the charges migrate to, and we can see that this happens within a few femtoseconds," Emad Aziz stresses. The result also has major repercus-sions for the interpretation of X-ray absorption spectra in general.
For their experiments, the group used a specially developed flow cell that also allows them to study biological samples by X-ray in their natural environment that is in dissolved form.
|Contact: Dr. Emad Flear Aziz Bekhit|
Helmholtz Association of German Research Centres