| 1. |
- Velkov, Zhivko A., et al.
(author)
-
Melatonin : Quantum-chemical and biochemical investigation of antioxidant activity
- 2009
-
In: European Journal of Medicinal Chemistry. - : Elsevier. - 0223-5234 .- 1768-3254. ; 44:7, s. 2834-2839
-
Journal article (peer-reviewed)abstract
- Experimental and theoretical investigation of the antioxidant activity of melatonin is carried out. The theoretical approach comprises the evaluation of several appropriate descriptors of scavenging activity with the help of quantum-chemistry methods. The values obtained are compared with available data for substances with established antioxidant properties. One of the most widely used markers for in vivo free radical oxidation processes is malondialdehyde (MDA) as an end product of membrane lipid peroxidation. Experimental support of the computed scavenging parameters is provided by estimation of the effect of supplementary melatonin therapy on the plasma levels of MDA in CRF patients on maintenance HD therapy. Different reaction paths have been considered and related to the obtained data, allowing speculations about the reaction mechanism and the antioxidant potential of melatonin for practical purposes.
|
|
| 2. |
- Feifel, R., et al.
(author)
-
X-ray absorption and resonant Auger spectroscopy of O(2) in the vicinity of the O 1s ->sigma* resonance : Experiment and theory
- 2008
-
In: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 128:6
-
Journal article (peer-reviewed)abstract
- We report on an experimental and theoretical investigation of x-ray absorption and resonant Auger electron spectra of gas phase O(2) recorded in the vicinity of the O 1s ->sigma* excitation region. Our investigation shows that core excitation takes place in a region with multiple crossings of potential energy curves of the excited states. We find a complete breakdown of the diabatic picture for this part of the x-ray absorption spectrum, which allows us to assign an hitherto unexplained fine structure in this spectral region. The experimental Auger data reveal an extended vibrational progression, for the outermost singly ionized X (2)Pi(g) final state, which exhibits strong changes in spectral shape within a short range of photon energy detuning (0 eV>Omega>-0.7 eV). To explain the experimental resonant Auger electron spectra, we use a mixed adiabatic/diabatic picture selecting crossing points according to the strength of the electronic coupling. Reasonable agreement is found between experiment and theory even though the nonadiabatic couplings are neglected. The resonant Auger electron scattering, which is essentially due to decay from dissociative core-excited states, is accompanied by strong lifetime-vibrational and intermediate electronic state interferences as well as an interference with the direct photoionization channel. The overall agreement between the experimental Auger spectra and the calculated spectra supports the mixed diabatic/adiabatic picture.
|
|
| 3. |
- Hikosaka, Y., et al.
(author)
-
X-ray absorption measured in the resonant Auger scattering mode
- 2008
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 101:7
-
Journal article (peer-reviewed)abstract
- We report both experimental and theoretical studies on x-ray absorption measured in the resonant Auger scattering mode of gas phase carbon monoxide near the O1s -> 2 pi region. Both experiment and theory display a crucial difference between the x-ray absorption profiles obtained in the conventional and resonant scattering modes. Lifetime vibrational interference is the main source of the difference. It is demonstrated that such interference, which arises from a coherent excitation to overlapping intermediate levels, ruins the idea for obtaining x-ray absorption spectra in a lifetime broadening free regime.
|
|
| 4. |
- Liu, Ji-Cai, et al.
(author)
-
Resonant inelastic X-ray Raman scattering induced by Rabi flopping of core holes
- 2008
-
In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 453:1-3, s. 117-121
-
Journal article (peer-reviewed)abstract
- A new scheme of X-ray pump-probe experiment is suggested in this Letter, namely resonant inelastic X-ray scattering accompanied by core-hole hopping induced by a strong laser field. In particular, we study the dynamics of X-ray Raman scattering of N-2 molecules in a strong IR field. The laser-induced mixing of the core holes of opposite parities opens symmetry forbidden scattering channels. The strength of the symmetry forbidden channels strongly depends on the interrelationship between the time of Rabi flopping of the core holes and the scattering duration or the duration of the X-ray pulse.
|
|
| 5. |
- Liu, Ji-Cai, et al.
(author)
-
Symmetry-forbidden x-ray Raman scattering induced by a strong infrared-laser field
- 2008
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 77:4, s. 043405-
-
Journal article (peer-reviewed)abstract
- Resonant inelastic x-ray scattering accompanied by core-hole hopping induced by a strong infrared-laser field is studied for the nitrogen molecule. This process involves a strong laser-field-induced promotion of ungerade core holes created by a weak x-ray pulse to a gerade core level, which opens symmetry-forbidden scattering channels and gives rise to new features in the x-ray scattering spectrum. The core-hole hopping within the short lifetime of the core-excited state required for observation of the described process can be achieved at moderate intensities of the infrared field (similar to 10(12) W/cm(2)) because of the large transition dipole moment between the relevant core levels. The dynamics of resonant inelastic x-ray scattering assisted by change of core-hole parity is studied in detail versus the intensity, detuning, phase, and duration of the incident infrared-laser and x-ray pulses.
|
|
| 6. |
- Samoc, Marek, et al.
(author)
-
Cubic Nonlinear Optical Properties of Platinum-Terminated Polyynediyl Chains
- 2008
-
In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 47:21, s. 9946-9957
-
Journal article (peer-reviewed)abstract
- The wavelength dependence of the cubic nonlinearity of ligated platinum-terminated polyynes trans, trans-{(P-MeC6H4)(3)P}(2)(p-MeC6H4)Pt(C C)(n)Pt(p-C6H4Me){P(p-C6H4Me)(3)}(2) (n = 3-6, 8, 10, 12) has been examined by femtosecond Z-scan studies in the wavelength range 520-1500 nm and the results rationalized by density functional theory calculations on the model complexes trans, trans-(H3P)(2)(C6H5)Pt(C C)(n)Pt(C6H5)(PH3)(2) (n = 2-8, 10, 12). Although the final states for one- and two-photon transitions are not the same in these centrosymmetric molecules, the Z-scan studies reveal coincidences in one-photon absorption with features in the frequency dependencies of both real and imaginary parts of the cubic hyperpolarizability, as well as inflections in the frequency dependencies of the real part of gamma that correspond to resonances in the imaginary part of gamma. The theoretical studies suggest that the linear absorption spectra are dominated by (XAg)-Ag-1 -> n(1)B(3u) transitions, with the first state of B-3u symmetry playing a steadily diminishing role upon oligoyne chain lengthening. The theoretical studies also predict a red-shift of two-photon absorption (TPA) profile with increasing conjugation length, and a significant enhancement on proceeding from the shortest to the longest chromophore, trends that are observed experimentally. The experimental low-energy TPA maxima for these complexes can be approximated by a simple Gaussian profile. The sp-carbon chain-length dependence of linear and nonlinear absorption maxima enable an estimate (neglecting saturation) of 660 and 1000 nm for the infinite carbon chain, carbyne.
|
|
| 7. |
- Sorensen, S. L., et al.
(author)
-
Electronic Doppler effect in resonant Auger decay of CO molecules upon excitation near a shake-up Pi resonance
- 2007
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - : APS. - 1050-2947 .- 1094-1622. ; 76:062704
-
Journal article (peer-reviewed)abstract
- Wepresent an experimental observation of the electronic Doppler effect inresonant Auger spectra upon core excitation slightly above the carbonK edge of the CO molecule. Thus the electronic Dopplereffect has been identified in above-threshold excitation, and in atransition of symmetry. Ab initio calculations of the potentialenergy curves of the relevant states of CO and thewave packet technique have been employed to provide a theoreticalbackground to the experimental studies. The weak feature around 299.4 eVin the photoabsorption spectrum, whose decay has been investigated bythe present experiment, is assigned to double (core-valence) excitations toC 1s shake-up states |1s1−1*2 with a strong dissociative character,and the Doppler splitting of the atomic peak has beenreproduced by the simulation.
|
|
| 8. |
|
|
| 9. |
- Velkov, Yasen, et al.
(author)
-
Origin of fine structures on the dissociative 1s ->sigma* resonance in X-ray absorption spectra of O-2
- 2009
-
In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 476:4-6, s. 147-150
-
Journal article (peer-reviewed)abstract
- We attempt to explain a puzzling long-tailed peak shape of the X-ray absorption spectrum of the oxygen molecule in the energy region around 539 eV taking into account the Rydberg-valence and vibronic couplings. The long-tailed feature is found to arise from two dissociative sigma* states and the sudden drop in intensity is related to decrease in transition dipole near the crossing point between the repulsive sigma* and weak 3s Rydberg states with the quartet ion cores. This is supported by numerical wave-packet simulations allowing for all interchannel couplings between the Rydberg and valence manifolds with the quartet and doublet ion cores in a diabatic representation of the core-excited states.
|
|
| 10. |
|
|
