Heme doming in ferric cytochrome c: Femtosecond xray absorption and x-ray emission studies

The photoinduced dynamics of ferric Cytochrome c was investigated by ultrafast non-resonant X-ray emission (XES) and X-Ray Absorption (XAS) spectroscopies, and a cascade through high spin states accompanied by heme doming are observed for the first time

Ultrafast Energy Transfer from Photoexcited Tryptophan to the Haem in Cytochrome c

We report femtosecond Fe K-edge absorption (XAS) and nonresonant X-ray emission (XES) spectra of ferric cytochrome C (Cyt c) upon excitation of the haem (>300 nm) or mixed excitation of the haem and tryptophan (<300 nm). The XAS and XES transients obtained in both excitation energy ranges show no evidence for electron transfer processes between photoexcited tryptophan (Trp) and the haem, but rather an ultrafast energy transfer, in agreement with previous ultrafast optical fluorescence and transient absorption studies. The reported (J. Phys. Chem. B 2011, 115 (46), 13723-13730) decay times of Trp fluorescence in ferrous (∼350 fs) and ferric (∼700 fs) Cyt c are among the shortest ever reported for Trp in a protein. The observed time scales cannot be rationalized in terms of Förster or Dexter energy transfer mechanisms and call for a more thorough theoretical investigation

Nonlinear XUV-optical transient grating spectroscopy at the Si L 2,3 –edge

Time-resolved transient grating (TG) spectroscopy facilitates detailed studies of electron dynamics and transport phenomena by means of a periodic excitation of matter with coherent ultrashort light pulses. Several current and next generation free-electron laser (FEL) facilities provide fully coherent pulses with few femtosecond pulse durations and extreme ultraviolet (XUV) photon energies. Thus, they allow for transient grating experiments with periodicities as small as tens of nanometers and with element specific photon energies. Here, we demonstrate the element specificity of XUV TG (X-TG) experiments by tuning the photon energy across the Si L₂,₃-edge of Si₃N₄. We observe a shortening of the signal decay when increasing the XUV photon energy above the absorption edge. The analysis of the wavelength dependent signal shows that the faster decay is driven by the increase in the charge carrier density. From the decay constants the interband Auger coefficient at elevated temperatures and high electron densities has been determined.Swiss National Science Foundation (SNF) (Grant 200021_165550/1

Hard X-ray transient grating spectroscopy on bismuth germanate

Optical-domain transient grating (TG) spectroscopy is a versatile background-free four-wave-mixing technique that is used to probe vibrational, magnetic and electronic degrees of freedom in the time domain1. The newly developed coherent X-ray free-electron laser sources allow its extension to the X-ray regime. X-rays offer multiple advantages for TG: their large penetration depth allows probing the bulk properties of materials, their element specificity can address core excited states, and their short wavelengths create excitation gratings with unprecedented momentum transfer and spatial resolution. Here, we demonstrate TG excitation in the hard X-ray range at 7.1 keV. In bismuth germanate (BGO), the non-resonant TG excitation generates coherent optical phonons detected as a function of time by diffraction of an optical probe pulse. This experiment demonstrates the ability to probe bulk properties of materials and paves the way for ultrafast coherent four-wave-mixing techniques using X-ray probes and involving nanoscale TG spatial periods