Optical excitation processes: general discussion

Abstract

Have you been able to carry out simultaneous time-resolved X-ray scattering and emission measurements in order to more rmly establish the mechanistic sequence and spin-structure correlations being proposed?Serhane Zerdane responded: Indeed, complementary experiments would provide valuable input, especially regarding correlated changes of spin-state and structure. When we performed the XANES experiment at LCLS, it was not possible to perform emission spectroscopy and scattering experiments simultaneously. We expect to perform these measurements during the next beamtime.Yorrick Boeije asked: Considering the 80 fs temporal resolution of the optical pump-probe measurements, how do you distinguish between local lattice torsion activation induced by (1) charge-transfer (CT) or (2) a process prior to chargetransfer, either optical excitation or the spin transition?Serhane Zerdane replied: For monitoring changes of electronic state and structure we used two complementary techniques: optical spectroscopy and X-ray spectroscopy (XANES). The time resolution was limited to 80 fs in time-resolved optical spectroscopy and this technique is indirectly sensitive to CT and spin transition through the associated electronic reorganizations. The time resolution of the XANES experiment was about 25 fs (ref. 1) and this technique is sensitive to both inter-metallic charge transfer (opposite shis for Co and Fe K edges) and spin transition (shis the rst extended X-ray absorption ne structure above the Co edge). In this way we could show that the spin transition occurs on the Co rst, and is followed by an intermetallic charge-transfer. 1