Probing molecular dynamics with free electron lasers

dwellnFree electron laser facilities provide unique opportunities to probe ultrafast dynamics. Their wide spectral range allows for element specific spectroscopy at the L- and K-edges of many important elements. In particular, we are keen on the K-edges of carbon, nitrogen and oxygen, the most important ingredients of organic molecules.

Element sensitive spectroscopy means, the core level binding energies of different elements have an appreciable energy difference and are clearly separable. The K-edges of C,N, and O are separated by more 100 eV.

The image shows binding energies of C. N and O 1s electrons.  In addition, the tight binding potential forces the 1s states to be localized in a narrow range of a few picometers around the atom. The left column shows a cut through the orbital charge density of the molecular orbitals – the 1s orbitals are visible as ‘needles’ in the blue background. The valence orbitals, in contrast, are delocalized all over the molecules, as the typical surface plot of the orbitals in the right column shows.

Any transition from 1s to a valence level therefore is highly sensitive on the electronic structure at this particular atom. This is in stark contrast to valence-valence electron transitions.


We use this element and site sensitivity to deduce details on the molecular dynamics from the x-ray perspective.






  1. Probing Molecular Photoexcited Dynamics by Soft X-Rays
    M. Gühr in: Ultrafast Dynamics Driven by Intense Light Pulses, eds.: M. Kitzler S. Graefe (Springer, Heidelberg, 2016)
    link to article
  2. Ultrafast X-ray Auger Probing of photoexcited molecular dynamics
    B. K. McFarland, J. P. Farrell, S. Miyabe, F. Tarantelli, A. Aguilar, N. Berrah, C. Bostedt, J. D. Bozek, P.H. Bucksbaum, J. C. Castagna, R. N. Coffee, J. P. Cryan, L. Fang, R. Feifel, K. J. Gaffney, J. M. Glownia, T.J. Martinez, M. Mucke, B. Murphy, A. Natan, T. Osipov , V. S. Petrovic, S. Schorb, Th. Schultz, L. S. Spector, M. Swiggers, I. Tenney, S. Wang, J. L. White, W. White, and M. Gühr
    Nature Comm. 5, 4235 (2014)  
    link to article
  3. Experimental strategies for optical pump – soft x-ray probe experiments at the LCLS
    B. K. McFarland, N. Berrah, C. Bostedt, J. Bozek, P.H. Bucksbaum, J. C. Castagna, R. N. Coffee, J. Cryan, L. Fang, J. P. Farrell, R. Feifel, K. Gaffney, J. Glownia, T. Martinez, M. Mucke, B. Murphy, S. Miyabe, A. Natan, T. Osipov , V . Petrovic, S. Schorb, Th. Schultz, M. Swiggers, L. Spector, F. Tarantelli, I. Tenney, S. Wang, W. White, J. White, M. Gühr,
    J. Phys.: Conf. Ser. 488, 012015 (2014) 
    link to article