151 research outputs found
a view from modern soft X-ray spectroscopies
Soft X-ray spectroscopies are powerful tools for probing the local electronic
and molecular orbital structures of materials in different phases and various
environments. While modern spectroscopic tools using soft X-ray synchrotron
photons perspicuously reveal the molecular orbital (MO) structure in detail,
structures remain widely unknown in the liquid phase since many of these
techniques could only be applied to solutions very recently. Furthermore, the
interactions and dynamics of molecules in the liquid phase are especially
complicated compared to those in gas and solid phases and thereby impede the
understanding of functional materials in solution. This review presents recent
developments using soft X-ray radiation for probing the electronic structure
of ions and molecules in solution. The presented X-ray absorption, emission,
and photo-electron spectroscopy studies exhibit the powerful contributions of
soft X-ray liquid spectroscopies in the last few years
recent techniques and applications using soft X-ray spectroscopy
The aim of a more precise knowledge about molecular structures and the nature
of chemical bonds is the driving force behind the development of numerous
experimental methods and theories. Recent soft X-ray based techniques provide
novel opportunities for tackling the structure and the dynamics of chemical
and biochemical systems in solution. In our research group we are developing
experimental methods for mapping the electronic structure and dynamics of
molecular systems in solution during bond-building and breaking using soft
X-ray absorption and emission spectroscopy. The combination of such recent
developments with conventional spectroscopy as well as theoretical modeling
allows us to address open questions about hydrogen bonds, thermodynamics and
active centers of biological systems. Based on the core-hole clock and
pump–probe spectroscopy dynamics on the time scale from sub-femtoseconds up to
picoseconds can be revealed
Multi-reference approach to the calculation of photoelectron spectra including spin-orbit coupling
X-ray photoelectron spectra provide a wealth of information on the electronic
structure. The extraction of molecular details requires adequate theoretical
methods, which in case of transition metal complexes has to account for effects
due to the multi-configurational and spin-mixed nature of the many-electron
wave function. Here, the Restricted Active Space Self-Consistent Field method
including spin-orbit coupling is used to cope with this challenge and to
calculate valence and core photoelectron spectra. The intensities are estimated
within the frameworks of the Dyson orbital formalism and the sudden
approximation. Thereby, we utilize an efficient computational algorithm that is
based on a biorthonormal basis transformation. The approach is applied to the
valence photoionization of the gas phase water molecule and to the core
ionization spectrum of the complex.
The results show good agreement with the experimental data obtained in this
work, whereas the sudden approximation demonstrates distinct deviations from
experiments
an iron L-edge X-ray absorption study of the active centre
Iron L-edge X-ray absorption spectra of the active centre of myoglobin in the
met-form, in the reduced form and upon ligation to O2, CO, NO and CN are
presented. The strength of ligation with the iron centre is finger-printed
through the variation of the L3 : L2 intensity ratio. Charge Transfer
Multiplet calculations are performed and give qualitative information about
oxidation states as well as charge transfer
Multiplateau structure in photoemission spectra of strong-field ionization of dense media
Strong-field ionization of dense molecular gases in a short infrared laser
pulse is studied by means of photoelectron spectroscopy combined with a liquid
microjet technique. By increasing the gas density, we observe how the laser-
assisted electron scattering on neighboring particles becomes a dominant
mechanism of hot electron emission. The angle-resolved energy distributions of
rescattered electrons are obtained by analyzing the density dependency of
emission spectra. A semiclassical consideration of electron trajectories is
shown to provide a good description of experimental spectra. The model
predicts the existence of four energy plateaus. Two cutoffs at higher energies
are evident in the spectra
Soft-X-Ray Absorption Spectroscopy and Ab Initio Calculations
Nonradiative decay channels in the L-edge fluorescence yield spectra from
transition-metal–aqueous solutions give rise to spectral distortions with
respect to x-ray transmission spectra. Their origin is unraveled here using
partial and inverse partial fluorescence yields on the microjet combined with
multireference ab initio electronic structure calculations. Comparing Fe2+,
Fe3+, and Co2+ systems we demonstrate and quantify unequivocally the state-
dependent electron delocalization within the manifold of d orbitals as one
origin of this observation
Erratum: “Multi-reference approach to the calculation of photoelectron spectra including spin-orbit coupling” [J. Chem. Phys. 143, 074104 (2015)]
spin-state and metal coordination revealed from resonant inelastic X-ray scattering and electronic structure calculations
The local electronic structure of the cobalt centre-ion of Co(III)
protoporphyrin IX chloride dissolved in dimethyl sulfoxide (DMSO) liquid
solution is studied by resonant inelastic X-ray scattering (RIXS) spectroscopy
at the cobalt L-edge. The resulting cobalt 2p partial-fluorescence-yield (PFY)
X-ray absorption (XA) spectrum, integrated from RIXS spectra, is simulated for
various possible spin-states and coordination of the cobalt centre by using
the newly developed density functional theory/restricted open shell single
excitation configuration interaction (DFT/ROCIS) method. Comparison between
experiment and calculation shows that the cobalt ion (3d6 electronic
configuration) adopts a low-spin state with all six 3d electrons paired, and
the cobalt centre is either 5-coordinated by its natural ligands (one chloride
ion and four nitrogen atoms), or 6-coordinated, when binding to an oxygen atom
of a DMSO solvent molecule. Analysis of the measured RIXS spectra reveals weak
3d–3d electron correlation, and in addition a value of the local HOMO–LUMO gap
at the Co sites is obtained
Charge transfer to solvent dynamics in iodide aqueous solution studied at ionization threshold
We explore the early-time electronic relaxation in NaI aqueous solution
exposed to a short UV laser pulse. Rather than initiating the charge transfer
reaction by resonant photoexcitation of iodide, in the present time-resolved
photoelectron spectroscopy study the charge-transfer-to-solvent (CTTS) states
are populated via electronic excitation above the vacuum level. By analyzing
the temporal evolution of electron yields from ionization of two transient
species, assigned to CTTS and its first excited state, we determine both their
ultrafast population and relaxation dynamics. Comparison with resonant-
excitation studies shows that the highly excited initial states exhibit
similar relaxation characteristics as found for resonant excitation.
Implications for structure and dynamical response of the hydration cage are
discussed
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