81 research outputs found
K-shell x-ray spectroscopy of atomic nitrogen
Absolute {\it K}-shell photoionization cross sections for atomic nitrogen
have been obtained from both experiment and state-of-the-art theoretical
techniques. Due to the difficulty of creating a target of neutral atomic
nitrogen, no high-resolution {\it K}-edge spectroscopy measurements have been
reported for this important atom. Interplay between theory and experiment
enabled identification and characterization of the strong
resonance features throughout the threshold region. An experimental value
of 409.64 0.02 eV was determined for the {\it K}-shell binding energy.Comment: 4 pages, 2 graphs, 1 tabl
Near-Edge X‐ray Absorption Fine Structure Investigation of the Quasi-One-Dimensional Organic Conductor (TMTSF)2PF6
We present high-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the P L2/3 edges, F K edge, C K edge, and Se M2/3 edges of the quasi-one-dimensional (1D) conductor and superconductor (TMTSF)2PF6. NEXAFS allows probing the donor and acceptor moieties separately; spectra were recorded between room temperature (RT) and 30 K at normal incidence. Spectra taken around RT were also studied as a function of the angle (θ) between the electric field of the X-ray beam and the 1D conducting direction. In contrast with a previous study of the S L2/3-edges spectra in (TMTTF)2AsF6, the Se M2/3 edges of (TMTSF)2PF6 do not exhibit a well-resolved spectrum. Surprisingly, the C K-edge spectra contain three well-defined peaks exhibiting strong and nontrivial θ and temperature dependence. The nature of these peaks as well as those of the F K-edge spectra could be rationalized on the basis of first-principles DFT calculations. Despite the structural similarity, the NEXAFS spectra of (TMTSF)2PF6 and (TMTTF)2AsF6 exhibit important differences. In contrast with the case of (TMTTF)2AsF6, the F K-edge spectra of (TMTSF)2PF6 do not change with temperature despite stronger donor−anion interactions. All these features reveal subtle differences in the electronic structure of the TMTSF and TMTTF families of salts
Ultrafast charge transfer processes accompanying KLL Auger decay in aqueous KCl solution
X-ray photoelectron spectroscopy (XPS) and KLL Auger spectra of aqueous KCl
solution were measured for the K and Cl edges. While the XPS spectra of
potassium and chloride have similar structures, both exhibiting only weak
satellite structures near the main line, the Auger spectra of these
isoelectronic ions differ dramatically. A very strong satellite peak was found
in the K KLL Auger spectrum at the low kinetic energy side of the D
state. Using equivalent core models and ab initio calculations this spectral
structure was assigned to electron transfer processes from solvent water
molecules to the solvated K cation. Contrary to the potassium case, no
extra peak was found in the KLL Auger spectrum of solvated Cl indicating on
a strong dependence of the underlying processes on ionic charge. The observed
charge transfer processes are suggested to play an important role in charge
redistribution following single and multiple core-hole creation in atomic and
molecular systems placed into an environment
Ionization potentials of crystalline organic thin films: Position dependence due to molecular shape and charge redistribution
In addition to electronic polarization or charge redistribution, the shape of
neutral conjugated molecules yields position-dependent ionization potentials
and electron affinities in organic thin films. Self-consistent I(n) and A(n)
are computed in each layer n of 10-layer films of prototypical organics on a
metal. The depth dependence of I(n) is discussed at surfaces of anthracene, C60
and PTCDA. The shape contribution can be substantial, up to 0.5 eV, and comes
primarily from charge-quadrupole interactions.Comment: 13 pages, 4 figures, Accepted in Chem. Phys. Letter
O 1s excitation and ionization processes in the CO2 molecule studied via detection of low-energy fluorescence emission
Oxygen 1s excitation and ionization processes in the CO2 molecule have been studied with dispersed and non-dispersed fluorescence spectroscopy as well as with the vacuum ultraviolet (VUV) photon?photoion coincidence technique. The intensity of the neutral O emission line at 845 nm shows particular sensitivity to core-to-Rydberg excitations and core?valence double excitations, while shape resonances are suppressed. In contrast, the partial fluorescence yield in the wavelength window 300?650 nm and the excitation functions of selected O+ and C+ emission lines in the wavelength range 400?500 nm display all of the absorption features. The relative intensity of ionic emission in the visible range increases towards higher photon energies, which is attributed to O 1s shake-off photoionization. VUV photon?photoion coincidence spectra reveal major contributions from the C+ and O+ ions and a minor contribution from C2+. No conclusive changes in the intensity ratios among the different ions are observed above the O 1s threshold. The line shape of the VUV?O+ coincidence peak in the mass spectrum carries some information on the initial core excitatio
Observation of electron transfer mediated decay in aqueous solution
Photoionization is at the heart of X ray photoelectron spectroscopy XPS , which gives access to important information on a sample s local chemical environment. Local and non local electronic decay after photoionization in which the refilling of core holes results in electron emission from either the initially ionized species or a neighbour, respectively have been well studied. However, electron transfer mediated decay ETMD , which involves the refilling of a core hole by an electron from a neighbouring species, has not yet been observed in condensed phase. Here we report the experimental observation of ETMD in an aqueous LiCl solution by detecting characteristic secondary low energy electrons using liquid microjet soft XPS. Experimental results are interpreted using molecular dynamics and high level ab initio calculations. We show that both solvent molecules and counterions participate in the ETMD processes, and different ion associations have distinctive spectral fingerprints. Furthermore, ETMD spectra are sensitive to coordination numbers, ion solvent distances and solvent arrangemen
Surface behavior of amphiphiles in aqueous solution: a comparison between different pentanol isomers
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