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Y-P Sun,
A Pietzsch,
F Hennies, Z Rinkevicius,
H O Karlsson,
T Schmitt,
V N Strocov,
J Andersson,
B Kennedy,
J Schlappa,
A Föhlisch,
F Gel'mukhanov,
J-E Rubensson
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ABSTRACT: Resonant inelastic soft x-ray scattering spectra excited at the dissociative 1σg → 3σu resonance in gas-phase O2 are presented and discussed in terms of state-of-the-art molecular theory. A new selection rule due to internal spin coupling is established, facilitating a deep analysis of the valence excited final states. Furthermore, it is found that a commonly accepted symmetry selection rule due to orbital parity breaks down, as the core hole and excited electron swap parity, thereby opening the symmetry forbidden 3σg decay channel.
Journal of Physics B Atomic Molecular and Optical Physics 07/2011; 44(16):161002. · 1.88 Impact Factor
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A Pietzsch,
Y-P Sun,
F Hennies, Z Rinkevicius,
H O Karlsson,
T Schmitt,
V N Strocov,
J Andersson,
B Kennedy,
J Schlappa,
A Föhlisch,
J-E Rubensson,
F Gel'mukhanov
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ABSTRACT: Resonant inelastic soft x-ray scattering (RIXS) spectra excited at the 1σ(g) → 3σ(u) resonance in gas-phase O2 show excitations due to the nuclear degrees of freedom with up to 35 well-resolved discrete vibronic states and a continuum due to the kinetic energy distribution of the separated atoms. The RIXS profile demonstrates spatial quantum beats caused by two interfering wave packets with different momenta as the atoms separate. Thomson scattering strongly affects both the spectral profile and the scattering anisotropy.
Physical Review Letters 04/2011; 106(15):153004. · 7.37 Impact Factor
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ABSTRACT: Specific and basicity solvent effects on the visible near-infrared electronic transitions and the electron paramagnetic resonance (EPR) parameters of the copper(II) acetylacetonate complex, Cu(acac)(2), have been investigated at the density functional theory level. The computed absorption transitions as well as the EPR parameters show a strong dependence on the direct coordination environment around the Cu(II) complex. High solvatocromic shifts are observed for 3d-3d transitions, with the highest effect observed for the d(z(2))→d(xy) transition, which is red-shifted by 6000 cm(-1) and 9000 cm(-1) in water and pyridine solvent models, respectively. Compared to the electronic g-tensors, the hyperfine coupling constants of the Cu(acac)(2) complex show a more pronounced dependence on the effect of base strength of solvent. Overall, the present methodology satisfactorily models the solvent effect on the optical and magnetic properties of the Cu(acac)(2) complex, and theory and experiment agree sufficiently well to warrant the use of the computed optical and EPR parameters to elucidate the coordination environment of the Cu(II) systems in basic solutions.
The Journal of Physical Chemistry A 02/2011; · 2.95 Impact Factor
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ABSTRACT: The present work addresses the solvatochromic shift of phenol blue (PB) dye. For this purpose the results of Car-Parrinello molecular dynamics (CPMD) simulations for PB in gas phase are compared with results obtained for PB in water from CPMD hybrid quantum mechanics-molecular mechanics (CPMD-QM/MM) calculations. The absorption spectra were obtained using the intermediate neglect of differential overlap/spectroscopic-configuration interaction (INDO/CIS) method and were calculated for a multitude of configurations of the trajectory. The calculated lambda(max) for PB in gas phase was found to be about 535 nm, which is considerably lower than the lambda(max) reported for PB in nonpolar solvents. Different solvation shells for PB in water have been defined based on the solute-all-atoms and solvent center of mass radial distribution function (g(r(X-O))). The electronic excitation energies for PB computed in the presence of solvent molecules in an increasing number of solvation shells were calculated in a systematic way to evaluate their contributions to the solvatochrmic shift. The inclusion of solvent molecules in the hydration shell yields a lambda(max) of 640 nm, which contributes to almost 78% of the solvatochromic shift. The inclusion of solvent molecules up to 10 A in the g(r(X-O)) rdf yields a lambda(max) of 670 nm which is in good agreement with the experimentally reported value of 654-684 nm. Overall, the present study suggests that the combined CPMD-QM/MM and INDO-CIS approach can be used successfully to model solvatochromic shifts of organic dye molecules.
The Journal of chemical physics 06/2010; 132(23):234508. · 3.09 Impact Factor
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ABSTRACT: A detailed dynamical theory of photobleaching by periodical sequences of laser pulses is presented. The theory is used for interpretation of recent experiments with pyrylium salts. Our simulations are based on first-principles simulations of photoabsorption cross-sections and on empirical rate constants. Two competitive channels of photobleaching, namely, photobleaching from the lowest excited singlet and triplet states and from higher excited states, are found to explain different intensity dependences of the photobleaching rates in different samples. The process includes two-photon excitation from the ground state to the first or second excited singlet states and one-photon excitation from the first singlet or triplet states to higher excited states. The fluorescence follows double-exponential dynamics with two characteristic times. The first and the shorter one is the equilibrium settling time between the ground and the lowest triplet states. The second characteristic time, the time of photobleaching, is responsible for the long-term dynamics. The effective rate of photobleaching from the first excited singlet and lowest triplet states depends differently on the irradiance in comparison with the photobleaching in higher states. The first channel is characterized by a quadratic intensity dependence in contrast to the second channel that shows a cubic dependence. The competition between these photobleaching channels is very sensitive to the rate constants as well as to the repetition rate, the pulse duration, and the peak intensity. The double-exponential decay of the fluorescence is explained by the spatial inhomogeneity of the light beam. The findings in this work are discussed in terms of the possibility of using many-photon-induced photobleaching for new three-dimensional read-write devices.
The Journal of Physical Chemistry A 12/2007; 111(47):11961-75. · 2.95 Impact Factor
