Stimulated x-ray Raman scattering

Novel approaches to the study of light-induced chemical and structural dynamics have been made possible by the femtosecond X-ray free-electron laser (XFEL) that enables time-resolved X-ray diffraction and spectroscopy. In particular, Stimulated Resonant Inelastic X-Ray scattering (S-RIXS) is a promising technique which potentially allows to follow electronic wave packets or the coupled motion of the electronic and nuclear degrees of freedom on femtosecond timescales. The experimental implementation and the critical assessment of S-RIXS have established it as the building block of nonlinear x-ray spectroscopy. The high temporal and spatial resolution granted by S-RIXS renders it to study chemical processes such as intramolecular electron transfers. The importance of these reactions resides in their ubiquity in nature and their key role in fundamental natural processes. Our research aims at contributing to the understanding of such processes in simple model systems, e.g. NCS, with the ultimate ambition of extending our studies to molecules with pivotal biological importance such as DNA.

Example of potential scheme for the study of electron transfer in NCS. The S-RIXS process creates a localized wave-packet on N (blue wave in the figure). The propagation of the wave packet across the molecule results in changes in the properties of the neighboring atoms which are probed by means a subsequent x-ray probe pulse.

The hypothesis of charge and energy transfer of DNA is a well-known hypothesis with its role in oxidative damage and repair. Beyond that, due to the unique features of DNA, research in this direction opens up possible applications of DNA in nanoelectronics, material science and in general biotechnological engineering. The charge and energy transfer of DNA are modulated by its structure and dynamics; moreover, different structural ensembles (both primary and secondary) support different charge and energy transport mechanisms.
Much research has been done so far but suffers of the well-known labeling problem, where the labels might interfere with the dynamical mechanisms by virtue of their massive dimensions, or by lack of atomic resolution and specificity, when only valence electrons are probed. We want to follow specific atomic elements within DNA to diagnose and ultimately drive photon-induced chemical mechanisms by label-free tools. The coherent amplification of S-RIXS could facilitate the study of charge and energy transfers in chemically and biologically relevant samples.

Involved group members:

Alessandra Picchiotti
Emanuele Rossi