Speaker
Description
Development of new machine modes at large scale facilities like Free-Electron Lasers (FEL) opened new experimental possibilities to study X-ray induced dynamics. With the “fresh slice method”, two intense femtosecond X-ray pulses can be produced with independent and tunable photon energy and time delay. This beam mode can be used in pump-probe schemes, exploiting the high target specificity of X-rays combined with femtosecond time resolution to study dissociation dynamics for instance. Here, we demonstrate the capabilities of the Maloja endstation to perform ultrafast X-ray spectroscopic measurements with the 2-color mode developed for the soft X-ray Athos beamline at SwissFEL [1].
In the first presented experiment, X-ray Photoelectron Spectroscopy (XPS) was employed to study the core-excited ultrafast dynamics of CF4. The XPS differential map is presented in Figure 1 and shows, in addition to the CF4 ground-state bleach at 694eV, a very fast transient feature at 718eV that thereafter feeds into two different peaks CF3+ at 705eV and F+ at 727eV.
In a more recent beamtime, we performed X-ray Absorption Spectroscopy (XAS) of weakly bound water clusters to study the ultrafast relaxation pathways and competition of non-local processes like Intermolecular Coulombic Decay (ICD) and Proton Transfer (PT). We were able to disentangle an almost instantaneous signal, that we attribute to ICD, from a delayed channel corresponding to PT.
These experiments highlight the ability of Maloja to use an all-X-ray pump-probe scheme to investigate ultrafast processes with different targets (gas or molecular clusters) and observables (photoelectrons or fragmented ions).
References:
1- Prat, E. et al. Widely tunable two-color x-ray free-electron laser pulses. Phys Rev Res 4, (2022).
| Scientific Topics | AMO Physics |
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