| 1. |
- Atak, Kaan, et al.
(author)
-
The Chemical Bond in Carbonyl and Sulfinyl Groups Studied by Soft X-ray Spectroscopy and ab Initio Calculations
- 2012
-
In: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 13:13, s. 3106-3111
-
Journal article (peer-reviewed)abstract
- The polar character of the sulfinyl bond, which determines many of the properties of dimethyl sulfoxide (DMSO), is a result of charge transfer in low-lying π-type orbitals. This characteristic—together with the wide energy gap between the highest occupied and the lowest unoccupied molecular orbitals of this substance—makes DMSO a relatively inert aprotic solvent with strong nucleophilicity and electrophilicity.
|
|
| 2. |
- Fransson, Thomas, et al.
(author)
-
X-ray and Electron Spectroscopy of Water
- 2016
-
In: Chemical Reviews. - : AMER CHEMICAL SOC. - 0009-2665 .- 1520-6890. ; 116:13, s. 7551-7569
-
Research review (peer-reviewed)abstract
- Here we present an overview of recent developments of X-ray and electron spectroscopy to probe water at different temperatures. Photon-induced ionization followed by detection of electrons from either the 0 is level or the valence band is the basis of photoelectron spectroscopy. Excitation between the 0 is and the unoccupied states or occupied states is utilized in X-ray absorption and X-ray emission spectroscopies. These techniques probe the electronic structure of the liquid phase and show sensitivity to the local hydrogen-bonding structure. Both experimental aspects related to the measurements and theoretical simulations to assist in the interpretation are discussed in detail. Different model systems are presented such as the different bulk phases of ice and various adsorbed monolayer structures on metal surfaces.
|
|
| 3. |
- Hua, Weijie, et al.
(author)
-
Systematic Study of Soft X-ray Spectra of Poly(Dg)center dot Poly(Dc) and Poly(Da)center dot Poly(Dt) DNA Duplexes
- 2010
-
In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:20, s. 7016-7021
-
Journal article (peer-reviewed)abstract
- In the present work, we have undertaken a combined experimental and theoretical study of X-ray spectroscopies for DNA base pairs, more precisely near-edge X-ray absorption, X-ray emission, and resonant inelastic X-ray scattering applied to poly(dG)center dot poly(dC) and poly(dA)center dot poly(dT) DNA duplexes. We have derived several conclusions on the nature of these X-ray spectra: the stacking of pairs has very little influence on the spectra; the spectra of a DNA composed of mixed Watson-Crick base pairs are well reproduced by linear combinations of GC and AT base pairs involved; the amine and imine nitrogens show noticeable differences as building blocks in the absorption, emission, and resonant emission spectra. The calculated spectra are in good agreement with experimental results. The ramifications of these conclusions for the use of X-ray spectroscopy for DNA are discussed.
|
|
| 4. |
- Kimberg, Victor, et al.
(author)
-
Calculation of K-edge circular dichroism of amino acids : Comparison of random phase approximation with other methods
- 2007
-
In: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 126:24
-
Journal article (peer-reviewed)abstract
- Soft x-ray natural circular dichroism of amino acids is studied by means of ab initio methods. Several approaches to evaluate the oscillator and rotary strengths of core-to-valence excitations are compared from the viewpoint of basis set dependence: ground-state Hartree-Fock (HF) orbital set employed in (i) random phase approximation (RPA), (ii) static exchange approach (STEX) (unrelaxed), (iii) core-ionized state HF orbital set applied in STEX (relaxed), and (iv) HF excited state orbital set for each core-to-valence excited state. Furthermore in (i) the PRA in the framework of the density functional method (DFT) is compared with the RPA where the ab initio HF orbital set is used. In (iv), the oscillator and rotary strengths evaluated by different orbital sets for the initial and final states, namely, nonorthogonal ground-state and core-excited HF orbitals, are compared with those evaluated by using the core-excited HF orbital set to describe the initial (ground) state. It was shown that, among considered methods, the RPA provides most consistent and less time-consuming results for circular dichroism core excitation spectra. Discussion of the low energy part of K edge circular dichroism spectra of five common amino acids obtained with the help of RPA is presented.
|
|
| 5. |
- Kimberg, Victor, et al.
(author)
-
Rydberg-valence mixing and interchannel coupling in resonant oxygen 1s inelastic x-ray scattering of O_2
- 2012
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 85:3
-
Journal article (peer-reviewed)abstract
- Rydberg-valence (RV) mixing and doublet-quartet (DQ) interchannel coupling in the core-excited states of triplet open-shell O2 are experimentally and theoretically unveiled through the resonant inelastic x-ray scattering around the O 1s→σ∗u resonance. Ab initio calculations explain complicated excitation energy dependence of the spectral profile by the interplay of the DQ interchannel coupling under the presence of the RV mixing. Complicated intermediate states with valence and/or Rydberg character are successfully analyzed through the filtering of pure valence and pure Rydberg final states.
|
|
| 6. |
- Kimberg, Victor, et al.
(author)
-
Theoretical studies of angle-resolved ion yield spectra of core-to-valence transitions of acetylene
- 2009
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130:11
-
Journal article (peer-reviewed)abstract
- Recent experimental results on angle-resolved photoion-yield spectroscopy (ARPIS) spectra near the core-to-valence excitation in acetylene show significant anisotropies in the spectral profile measured at 0 degrees and 90 degrees regarding to the polarization direction of x-ray photons. In the present work, a theoretical model is proposed to simulate the fine structure and anisotropy in ARPIS. This employs two-dimensional potential energy surfaces of the ground and core-excited states, as well as transition dipole moments, including symmetric and antisymmetric bending modes to account for Duschinsky effect. The ARPIS is simulated by evaluation of the ion flux, which is found as a projection of the excited state wave packet on a particular direction in the molecular frame. Numerical simulations explain qualitatively the angular dependence of the experimental spectra of the 1s -> 1 pi(*)(g) and 1s -> 3 sigma(*)(u) transitions. The effects of the lifetime of the core-excited state, the direction of the ion flux, and the transition dipole moment are discussed.
|
|
| 7. |
- Lindgren, Andreas, et al.
(author)
-
Core localization and sigma( *) delocalization in the O 1s core-excited sulfur dioxide molecule.
- 2008
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:11
-
Journal article (peer-reviewed)abstract
- Electron-ion-ion coincidence measurements of sulfur dioxide at discrete resonances near the O 1s ionization edge are reported. The spectra are analyzed using a model based upon molecular symmetry and on the geometry of the molecule. We find clear evidence for molecular alignment that can be ascribed to symmetry properties of the ground and core-excited states. Configuration interaction (CI) calculations indicate geometry changes in accord with the measured spectra. For the SO(2) molecule, however, we find that the localized core hole does not produce measurable evidence for valence localization, since the transition dipole moment is not parallel to a breaking sigma(*) O-S bond, in contrast to the case of ozone. The dissociation behavior based upon the CI calculations using symmetry-broken orbitals while fixing a localized core-hole site is found to be nearly equivalent to that using symmetry-adapted orbitals. This implies that the core-localization effect is not strong enough to localize the sigma(*) valence orbital.
|
|
| 8. |
- Liu, Ji-Cai, et al.
(author)
-
Multimode Resonant Auger Scattering from the Ethene Molecule
- 2011
-
In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 115:18, s. 5103-5112
-
Journal article (peer-reviewed)abstract
- Resonant Auger spectra of ethene molecule have been measured with vibrational resolution at several excitation energies in the region of the C1s(-1)1b(2g)(π*) resonance. The main features observed in the experiment have been assigned and are accurately interpreted on the basis of ab initio multimode calculations. Theory explains the extended vibrational distribution of the resonant Auger spectra and its evolution as a function of the excitation energy by multimode excitation during the scattering process. As a result, the resonant Auger spectra display two qualitatively different spectral features following the Raman and non-Raman dispersion laws, respectively. Calculations show that two observed thresholds of formation of non-Raman spectral bands are related to the "double-edge" structure of the X-ray absorption spectrum.
|
|
| 9. |
- Miron, Catalin, et al.
(author)
-
Imaging molecular potentials using ultrahigh-resolution resonant photoemission
- 2012
-
In: Nature Physics. - 1745-2473 .- 1745-2481. ; 8:2, s. 135-138
-
Journal article (peer-reviewed)abstract
- Electron-density distributions and potential-energy surfaces are important for predicting the physical properties and chemical reactivity of molecular systems. Whereas angle-resolved photoelectron spectroscopy enables the reconstruction of molecular-orbital densities of condensed species(1), absorption or traditional photoelectron spectroscopy are widely employed to study molecular potentials of isolated species. However, the information they provide is often limited because not all vibrational substates are excited near the vertical electronic transitions from the ground state. Moreover, many electronic states cannot be observed owing to selection rules or low transition probabilities. In many other cases, the extraction of the potentials is impossible owing to the high densities of overlapping electronic states. Here we use resonant photoemission spectroscopy, where the absence of strict dipole selection rules in Auger decay enables access to a larger number of final states as compared with radiative decay. Furthermore, by populating highly excited vibrational substates in the intermediate core-excited state, it is possible to 'pull out' molecular states that were hidden by overlapping spectral regions before.
|
|
| 10. |
- Miron, Catalin, et al.
(author)
-
Vibrational Scattering Anisotropy Generated by Multichannel Quantum Interference
- 2010
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 105:9, s. 093002-
-
Journal article (peer-reviewed)abstract
- Based on angularly and vibrationally resolved electron spectroscopy measurements in acetylene, we report the first observation of anomalously strong vibrational anisotropy of resonant Auger scattering through the C 1s --> pi* excited state. We provide a theoretical model explaining the new phenomenon by three coexisting interference effects: (i) interference between resonant and direct photoionization channels, (ii) interference of the scattering channels through the core-excited bending states with orthogonal orientation of the molecular orbitals, (iii) scattering through two wells of the double-well bending mode potential. The interplay of nuclear and electronic motions offers in this case a new type of nuclear wave packet interferometry sensitive to the anisotropy of nuclear dynamics: whether which-path information is available or not depends on the final vibrational state serving for path selection.
|
|
