W. Gawelda | Searcharxiv

arXiv2025

Laser-induced ultrafast structural transformations in thin Fe layer revealed by time-resolved X-ray diffraction

The ultrafast structural response of a thin iron film to sub-ps pulsed laser-induced heating has been investigated using time-resolved X-ray diffraction in the partial melting regime. A tetragonal distortion of the bcc-phase emerges at ~6 ps. Its formation is delayed relative to the initial heating (1-2 ps) and partial melting (2-5 ps) of the material, and controlled by the stress release in the quasi-instantaneously pressurized film. The distortion persists for at least 60 ps indicating the formation of a metastable bct phase between the equilibrium bcc and fcc phases.

cond-mat.mtrl-sci↗

arXiv2014

Hydration shell effects in the relaxation dynamics of photoexcited Fe-II complexes in water

We study the relaxation dynamics of photoexcited Fe-II complexes dissolved in water and identify the relaxation pathway which the molecular complex follows in presence of a hydration shell of bound water at the interface between the complex and the solvent. Starting from a low-spin state, the photoexcited complex can reach the high-spin state via a cascade of different possible transitions involving electronic as well as vibrational relaxation processes. By numerically exact path integral calculations for the relaxational dynamics of a continuous solvent model, we find that the vibrational life times of the intermittent states are of the order of a few ps. Since the electronic rearrangement in the complex occurs on the time scale of about 100 fs, we find that the complex first rearranges itself in a high-spin and highly excited vibrational state, before it relaxes its energy to the solvent via vibrational relaxation transitions. By this, the relaxation pathway can be clearly identified. We find that the life time of the vibrational states increases with the size of the complex (within a spherical model), but decreases with the thickness of the hydration shell, indicating that the hydration shell acts as an additional source of fluctuations.

physics.atm-clus↗