Probing Transient Valence Orbital Changes with Picosecond Valence-to-Core X-ray Emission Spectroscopy

Abstract

We probe the dynamics of valence electrons in photoexcited [Fe(terpy)2]2+ in solution to gain deeper insight into the Fe–ligand bond changes. We use hard X-ray emission spectroscopy (XES), which combines element specificity and high penetration with sensitivity to orbital structure, making it a powerful technique for molecular studies in a wide variety of environments. A picosecond-time-resolved measurement of the complete 1s X-ray emission spectrum captures the transient photoinduced changes and includes the weak valence-to-core (vtc) emission lines that correspond to transitions from occupied valence orbitals to the nascent core-hole. Vtc-XES offers particular insight into the molecular orbitals directly involved in the light-driven dynamics; a change in the metal–ligand orbital overlap results in an intensity reduction and a blue energy shift in agreement with our theoretical calculations and more subtle features at the highest energies reflect changes in the frontier orbital populations.

Valence‐to‐core X‐ray emission spectroscopy of titanium compounds using energy dispersive detectors

“…Comparative studies of vtc‐XES have been performed for different molecular complexes of first‐row transition metals such as titanium, 20–23 vanadium, 24 chromium, 25,26 manganese, 27–30 iron, 16,17 and cobalt 31 . Additionally, vtc‐XES has been applied to the study of 4d metals such as molybdenum 32 and niobium, 33 while groups at the Advanced Photon Source (APS) and the Linac Coherent Light Source (LCLS) extended vtc‐XES to the time domain by probing the dynamics of valence electrons in iron containing complexes 34–36 …”

“…31 Additionally, vtc-XES has been applied to the study of 4d metals such as molybdenum 32 and niobium, 33 while groups at the Advanced Photon Source (APS) and the Linac Coherent Light Source (LCLS) extended vtc-XES to the time domain by probing the dynamics of valence electrons in iron containing complexes. [34][35][36] To date, most vtc-XES measurements have been performed at high-brightness user facilities, such as synchrotrons, while a few groups have developed laboratory-based systems. [37][38][39][40][41][42][43][44] A constant in all previous vtc-XES measurements is the use of wavelength dispersive detection techniques, where specially designed gratings or crystals are used to spatially separate the different photon energies in the emission spectrum.…”

Using Ultrafast X-ray Spectroscopy To Address Questions in Ligand-Field Theory: The Excited State Spin and Structure of [Fe(dcpp)2]2+

“…More challenging has been the use of iron, the first-row congener of ruthenium. An enormous number of low-spin (LS) Fe(II) complexes are known, including the thoroughly studied Fe(II) polypyridyl complexes [Fe(bpy)3] 2+ 6-8 and [Fe(terpy)2] 2+ [9][10][11][12] . Their absorption spectra are dominated by strong MLCT transitions in the visible regime, however, these Fe(II)-based complexes have been difficult to employ in solar energy conversion schemes 5 due primarily to the fact the MLCT states convert to lower-lying metal-centered ligand-field (LF) states on the ~100 fs timescale 8,[13][14][15][16] .…”

Persistent Octahedral Coordination in Amorphous GeO2 Up to 100 GPa by Kβ′′Spiekermann1, Harder2, Gilmore3 et al. 2019Phys. Rev. X202250View full textAdd to dashboardCite

“…In this study, we address the ambiguity in the average germanium CN in compressed amorphous GeO 2 by a new approach on the basis of measured and computed valenceto-core x-ray emission spectroscopy (VTC XES) spectra of compressed GeO 2 . VTC XES has been mostly applied to 3d transition metal molecular complexes, where it is known to provide insight into the spin state and the type of the bonding ligand [25][26][27][28][29][30][31][32][33][34]. There have been only a few studies on nonmolecular crystalline compounds [35][36][37][38][39].…”