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Oscillator Strengths (oscillator + strength)
Selected AbstractsTime-resolved photoinduced Kerr rotation in semiconductor microcavityPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009Y. Mitsumori Abstract We studied photoinduced Kerr effect in cavity polaritons in a semiconductor microcavity by carefully measuring the time-resolved Kerr rotation and ellipticity spectra. The Kerr rotation angle of the microcavity polaritons is a hundred times larger than a conventional single quantum well. A spectral shape analysis of the observed spectra suggests that the photoindeced Kerr effect mainly results from a line broadening of the polarions due to spin-polarized polariton-polariton scattering. Enhancement in oscillator strength also contributes to the large rotation angle. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spectrally-resolved nonlinear spectroscopy of in-plane anisotropy in uniaxially-strained GaN epilayersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2005Satoru Adachi Abstract Spectrally-resolved four-wave mixing technique has revealed the internal structures of excitons in uniaxially strained gallium nitride films. Nonlinear response of four-wave mixing on the oscillator strength highlights the polarized excitons, and therefore allows us to map out the uniaxial strain field and the resultant anisotropic exchange splitting. Such a measurement gives a kind of crystalline analysis achieved in X-ray diffraction spectroscopy as well as information of the exciton fine structures including their temporal dynamics. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Benzo[b]phosphole-Containing ,-Electron Systems: Synthesis Based on an Intramolecular trans -Halophosphanylation and Some Insights into Their PropertiesCHEMISTRY - AN ASIAN JOURNAL, Issue 11 2009Aiko Fukazawa Dr. Abstract The intramolecular trans -halophosphanylation of 2-(aminophosphanyl)phenylacetylenes mediated by PBr3 followed by the oxidation with H2O2, produces 3-bromobenzo[b]phosphole oxide derivatives. This cyclization is also used for the synthesis of a 3-iodo derivative by conducting the reaction in the presence of LiI. Based on this synthetic method, various benzophosphole-containing ,-conjugated compounds, including a phosphoryl and methylene-bridged stilbene 10, 2,3,6,7-tetraphenylbenzo[1,2- b:4,5- b,]diphosphole- P,P, -dioxides 11, and their phosphine sulfide derivatives 12, are synthesized. The study of the structure,property relationships in a series of the bridged stilbenes, including a bis(methylene)-bridged stilbene 10, and a bis(phosphoryl)-bridged stilbene, reveals that as the contribution of the phosphoryl groups increased, the absorption and emission maxima substantially shift to longer wavelengths. The intrinsic substituent effects of the phosphoryl group in this skeleton are to decrease the oscillator strength of the electronic transition and thus decrease the radiative decay rate constants from the singlet excited state. Nevertheless, these compounds maintain high fluorescence quantum yields (,F>0.8) owing to the significantly retarded nonradiative decay process. In the study of the benzodiphosphole derivatives 11 and 12, their cyclic voltammetry revealed that both of the phosphoryl and phosphine sulfide derivatives have low reduction potentials (,1.7 to ,1.8,V vs ferrocene/ferrocenium couple) with the high reversibility of the redox waves. These compounds also showed high thermal stabilities with the high glass transition temperatures of 147,159,°C, indicative of their potential utilities as amorphous materials. [source] Effect of the Complexant Shape on the Large First Hyperpolarizability of Alkalides Li+(NH3)4M,,CHEMPHYSCHEM, Issue 8 2006Ying-Qi Jing Abstract The effect of complexant shape effect on the first hyperpolarizability ,0 of alkalides Li+(NH3)4M, (M=Li, Na, K) was explored. At the MP2/6-311++G level, Li+(NH3)4M, (M=Li, Na, K) have considerable ,0 values due to excess electrons from chemical doping and charge transfer. By comparison with the alkalides Li+(calix[4]pyrrole)M,, a complexant shape effect in Li+(NH3)4M, is detected. The ,0 values of Li+(NH3)4M, with the "smaller", inorganic, Td -symmetric (NH3)4 complexant are more than four times larger than those of Li+(calix[4]pyrrole)M, with the "larger", organic C4v -symmetric calix[4]pyrrole complexant. The ratios of the ,0 values of Li+(NH3)4M, and Li+(calix[4]pyrrole)M, are 6.57 (M=Li,), 6.55 (M=Na), and 5.17 (M=K). In the Li+(NH3)4M, systems, the NBO charge and oscillator strength are found to monotonically depend on the atomic number of the alkali metal anion. The order of the NBO charges of the alkali anions M, is ,0.667 (M=Li,)>,0.644 (M=Na)>,0.514 (M=K), while the order of the oscillator strengths in the crucial transition is 0.351 (M=Li,)<0.360 (M=Na)<0.467 (M=K). This indicates that complexant shape effects are strong, and consequently the ,0 values of Li+(NH3)4M, are found to be ,0=70,295 (M=Li,)<96,780 (M=Na)<185,805 a.u. (M=K). This work reveals that the use of a high-symmetry complexant is an important factor that should be taken into account when enhancing the first hyperpolarizability of alkalides by chemical doping. [source] UV Spectra and Excitation Delocalization in DNA: Influence of the Spectral WidthCHEMPHYSCHEM, Issue 7 2005Emanuela Emanuele Abstract The singlet excited states of the model DNA duplex (dA)10.(dT)10 are studied. Calculations are performed in the exciton theory framework. Molecular dynamics calculations provide the duplex geometry. The dipolar coupling is determined using atomic transition charges. The monomer transition energies are simulated by Gaussian functions resembling the absorption bands of nucleosides in aqueous solutions. Most of the excited states are found to be delocalized over at least two bases and result from the mixing of different monomer states. Their properties are only weakly affected by conformational changes of the double helix. On average, the highest oscillator strength is carried by the upper eigenstates. The duplex absorption spectra are shifted a few nanometers to higher energies with respect to the spectra of noninteracting monomers. The states with larger spatial extent are located close to the maximum of the absorption spectrum. [source] The electronically excited states of RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine): Vertical excitationsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2009Itamar Borges Jr Abstract The RDX molecule, hexahydro-1,3,5-trinitro-1,3,5-triazine, is a key component for several energetic materials, which have important practical applications as explosives. A systematic study of the electronic excited states of RDX in gas phase using time-dependent density functional theory (TDDFT), algebraic diagrammatic construction through second order method [ADC (2)], and resolution of the identity coupled-cluster singles and doubles method (RI-CC2) was carried out. Transition energies and optical oscillator strengths were computed for a maximum of 40 transitions. RI-CC2 and ADC (2) predict a spectrum shaped by three intense ,-,* transitions, two with charge transfer and one with localized character. TDDFT fails in the description of the charge transfer states. The low-energy band of the experimental UV spectrum of RDX is assigned to the first charge transfer state. Two alternative assignments of the high-energy band are proposed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Theoretical study on the second-order nonlinear optical properties of nonconjugated D-,-A chromophoresINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 7 2009Guochun Yang Abstract Density functional theory calculations have been carried out on nonconjugated D-,-A chromophores to investigate the different electron donors and conjugated bridges effects on the molecular nonlinear optical response. The results show that the large second-order polarizability values can be achieved through careful combination of available electron donors, conjugated bridges for our studied nonconjugated D-,-A chromophores. The calculations also provide a clear explanation for the second-order polarizability changes from the standpoint of transition energies, oscillator strengths, electron density difference, and bond length alternation. Solvent effect has great influence on the second-order polarizability and electronic absorption spectrum. It is hoped that the results presented in this article will give some hints to the interrelated studies. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Theoretical calculations of transition probabilities and oscillator strengths for Ti III and Ti IVINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2009Tian-Yi Zhang Abstract Due to the complicated electronic configuration of atoms and ions of the transition metal elements, the studies for properties such as transition probabilities and oscillator strengths for these atoms and ions are not systematic. Because of the existence in a variety of stellar objects and wide use in the field of astrophysics, titanium has long been of interest for many researchers. In this article within the Weakest Bound Electron Potential Model (WBEPM) theory, comprehensive set of calculations for transition probabilities and oscillator strengths for Ti III and Ti IV are performed. Many of our results had no previous experimental or theoretical values, so these predictive results could be of some value to the workers in this field. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Photoabsorption processes in nitrous oxide and formaldehydeINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2001I. Martín Abstract Absorption oscillator strengths and photoionization cross sections for electronic transitions involving Rydberg states that are relevant to the photochemistry of N2O and H2CO are reported. These compounds have been found to play an important role in the evolution of Earth's upper atmosphere. However, the difficulties encoutered in both laboratory measurements and theoretical calculations on the photoabsorption of these compounds are responsible for the scarcity of data in the literature. The present calculations have been performed with the molecular-adapted quantum defect orbital (MQDO) method, of which the adequacy for this type of studies has recently been assessed. A comparative analysis of the photoabsorption intensities in the molecules and their constituting atoms has enabled us to predict the variation of the extent of atomic character of the molecular Rydberg orbitals with the degree of excitation. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 [source] Time-dependent density functional calculations of the Q-like bands of phenylene-linked free-base and zinc porphyrin dimersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2001Yoichi Yamaguchi Abstract Time-dependent density functional theory (TDDFT) calculations have been performed on the excitation energies and oscillator strengths of the Q-like bands of three structural isomers of phenylene-linked free-base (FBP) and zinc (ZnP) porphyrin dimers. The TDDFT calculated results on the low-lying excited states of the reference monomers, FBP and ZnP, are in excellent agreement with previously calculated and experimental results. It is found that the 1,3- and 1,4-phenylene-linked dimers have monomerlike Q bands that are slightly red-shifted compared to the monomers and new Q, bands comprised of the cross-linked excitations from the FBP (ZnP) ring to the ZnP (FBP) ring at considerably lower energies than the monomer Q bands. For the 1,2-phenylene-linked dimer, the direct ,,, interaction between porphyrin rings caused by the van der Waals repulsion between them provides strong mixing of the Q, bands with the Q bands, which causes its minimum excitation energy to be red-shifted by 0.05 eV compared to the other isomers. The oscillator strengths of the Q, bands are also unexpectedly found to be as strong as those of the Q bands in the dimers. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 338,347, 2001 [source] QM/MM calculation of solvent effects on absorption spectra of guanineJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2010Maja Parac Abstract Electronic spectra of guanine in the gas phase and in water were studied by quantum mechanical/molecular mechanical (QM/MM) methods. Geometries for the excited-state calculations were extracted from ground-state molecular dynamics (MD) simulations using the self-consistent-charge density functional tight binding (SCC-DFTB) method for the QM region and the TIP3P force field for the water environment. Theoretical absorption spectra were generated from excitation energies and oscillator strengths calculated for 50 to 500 MD snapshots of guanine in the gas phase (QM) and in solution (QM/MM). The excited-state calculations used time-dependent density functional theory (TDDFT) and the DFT-based multireference configuration interaction (DFT/MRCI) method of Grimme and Waletzke, in combination with two basis sets. Our investigation covered keto-N7H and keto-N9H guanine, with particular focus on solvent effects in the low-energy spectrum of the keto-N9H tautomer. When compared with the vertical excitation energies of gas-phase guanine at the optimized DFT (B3LYP/TZVP) geometry, the maxima in the computed solution spectra are shifted by several tenths of an eV. Three effects contribute: the use of SCC-DFTB-based rather than B3LYP-based geometries in the MD snapshots (red shift of ca. 0.1 eV), explicit inclusion of nuclear motion through the MD snapshots (red shift of ca. 0.1 eV), and intrinsic solvent effects (differences in the absorption maxima in the computed gas-phase and solution spectra, typically ca. 0.1,0.3 eV). A detailed analysis of the results indicates that the intrinsic solvent effects arise both from solvent-induced structural changes and from electrostatic solute,solvent interactions, the latter being dominant. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010 [source] Radiative transitions of the helium atom in highly magnetized neutron star atmospheresMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Z. Medin ABSTRACT Recent observations of thermally emitting isolated neutron stars revealed spectral features that could be interpreted as radiative transitions of He in a magnetized neutron star atmosphere. We present Hartree,Fock calculations of the polarization-dependent photoionization cross-sections of the He atom in strong magnetic fields ranging from 1012 to 1014 G. Convenient fitting formulae for the cross-sections are given along with the related oscillator strengths for various bound,bound transitions. The effects of finite nucleus mass on the radiative absorption cross-sections are examined using perturbation theory. [source] Experimental Ti i oscillator strengths and their application to cool star analysisMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006R. J. Blackwell-Whitehead ABSTRACT We report experimental oscillator strengths for 88 Ti i transitions covering the wavelength range 465,3892 nm, 67 of which had no previous experimental values. Radiative lifetimes for 13 energy levels, including the low energy levels 3d2(3F) 4s4p (3P) z 5D°j, have been measured using time-resolved laser-induced fluorescence. Intensity-calibrated Ti i spectra have been measured using Fourier transform spectroscopy to determine branching fractions for the decay channels of these levels. The branching fractions are combined with the radiative lifetimes to yield absolute transition probabilities and oscillator strengths. Our measurements include 50 transitions in the previously unobserved infrared region , > 1.0 ,m, a region of particular interest to the analysis of cool stars and brown dwarfs. [source] The K, complex of He-like iron with dielectronic satellitesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2001Justin Oelgoetz It is shown that the dielectronic satellites (DES) dominate X-ray spectral formation in the 6.7-keV K, complex of Fe xxv at temperatures below that of maximum abundance in collisional ionization equilibrium Tm. Owing to their extreme temperature sensitivity, the DES are excellent spectral diagnostics for in photoionized, collisional or hybrid plasmas; whereas the forbidden, intercombination and resonance lines of Fe xxv are not. A diagnostic line ratio GD(T) is defined including the DES and the lines, with parameters from new relativistic atomic calculations. The DES absorption resonance strengths may be obtained from differential oscillator strengths, possibly to yield the column densities. The DES contribution to highly ionized Fe should be of interest for models of redward broadening of K, features, ionized accretion discs, accretion flows and K, temporal-temperature variability in AGN. [source] Energy loss of swift H and He projectiles in Al, Si, Ni and Cu targetsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2008Cristian D. Denton Abstract We have calculated the stopping power of Al, Si, Ni and Cu for swift H and He ion beams. Furthermore, the energy loss straggling corresponding to Ni is also evaluated. The dielectric formalism is used combined with the MELF-GOS method, which describes the energy loss function of the target by a linear combination of Mermin type energy loss functions for the electron outer-shell electrons and by generalized oscillator strengths for the electron inner-shell electrons. We take into account the corrections to the stopping power associated to capture and loss of electrons by the projectile as well as the polarization of the projectile charge density. The versatility of this method is illustrated by the good agreement between their predictions and the experimental results, which is observed for a wide range of projectile energies and targets with different electronic properties. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Strong excitonic mixing effect in asymmetric double quantum wells: On the optimization of electroabsorption modulatorsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2008Dong Kwon Kim Abstract We investigate the mixing of excitons originating in different subband pairs in asymmetric double quantum wells (ADQWs) in a range of electric field where the two lowest exciton states anticross. This excitonic mixing is mainly attributed to the Coulomb interactions between subbands and the valence-subband nonparabolicity. Results show that excluding the excitonic mixing effect results in significant error in both the energies and the oscillator strengths of the excitons in an ADQW with thick barrier (3 nm). Even in an ADQW with a fairly thin barrier (1.2 nm), the error in the oscillator strengths can be substantial, although the errors in the computed energies may be tolerable. We find that including the mixing of excitons is indispensable in optimizing the structures of the asymmetric double quantum well electroabsorption modulators. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Charge-density analysis of the ground state of a photochromic 1,10-phenanthroline zinc(II) bis(thiolate) complexACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010Stephan Scheins The charge density of the title compound was determined at 90,K, using a spherical crystal of 150,µm diameter. The proper treatment of the Zn atom in the pseudo-tetrahedral environment is considered in detail. A satisfactory refinement is only obtained when anharmonic Gram,Charlier parameters are included as variables in the refinement. A successful combined anharmonic/multipole refinement indicates a small polarization of the 4s shell in the anisotropic environment. One of the two toluenethiols is approximately ,-stacked with the phenanthroline ligand. A bond path is found connecting the two ligands. In addition the Zn,S bond to this ligand is slightly extended compared with the same bond to the second toluenethiol. A separate photocrystallographic and theoretical study indicates the long wavelength emission of the title compound to be due to a ligand-to-ligand charge transfer (LLCT) from a toluenethiol to the phenanthroline ligand. The charge-density results do not provide a basis for deciding which of the thiole ligands is the source of the transferred electron density. This result is in agreement with the theoretical calculations, which show comparable oscillator strengths for charge transfer from either of the ligands. [source] Localised magneto-optical collective excitations of impure grapheneANNALEN DER PHYSIK, Issue 12 2009A.M. Fischer Abstract We study optically-induced collective excitations of graphene in the presence of a strong perpendicular magnetic field and a single impurity. We determine the energies and absorption strengths of these excitations, which become localised on the impurity. Two different types of impurity are considered i. the long-range Coulomb impurity, ii. a ,-function impurity located at either an A or B graphene sublattice site. Both impurity types result in some bound states appearing both above and below the magnetoplasmon continuum, although the effect of the short-range impurity is less pronounced. The dependence of the energies and oscillator strengths of the bound states on the filling factor is investigated. [source] Metal-Induced Tautomerization of p - to o -Quinone Compounds: Experimental Evidence from CuI and ReI Complexes of Azophenine and DFT StudiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2004Stéphanie Frantz Abstract Azophenine (7,8-diphenyl-2,5-bis(phenylamino)- p -quinonediimine, Lp) reacts with [Cu(PPh3)4](BF4) or [Re(CO)5Cl] to yield the (Ph3P)2Cu+ or [(OC)3ClRe] complex of the tautomeric form 7,8-diphenyl-4,5-bis(phenylamino)- o -quinonediimine, Lo, as evident from structure determinations and from very intense metal-to-ligand charge transfer (MLCT) transitions in the visible region. Time-dependent DFT (TD-DFT) calculations on model complexes [(N,N)Re(CO)3Cl] confirm the spectroscopic results, showing considerably higher oscillator strengths of the MLCT transition for the o -quinonediimine complexes in comparison to compounds with N,N=1,4-dialkyl-1,4-diazabutadiene. The complexes are additionally stabilized through hydrogen bonding between two now ortho -positioned NHPh substituents and one fluoride of the BF4, anion (Cu complex) or the chloride ligand (Re complex). DFT Calculations on the model ligands p -quinonediimine or 2,5-diamino- p -quinonediimine and their ortho -quinonoid forms with and without Li+ or Cu+ are presented to discuss the relevance for metal-dependent quinoproteins. [source] Electronic Structure of the Ground and Excited States of ,-CarbolineCHEMPHYSCHEM, Issue 6 2008Vicente Pérez Mondéjar Abstract Coupled-cluster calculations are used to compute the energy of conversion between the neutral and the zwitterionic forms of ,-carboline. The stability of the different species is discussed in terms of charge separation and aromatic character, which is related to magnetic criteria. By means of a linear response formalism the vertical excitation energies and oscillator strengths of the lowest singlet states of both structures as well as of the cationic species are determined. General agreement of the relative position and intensity of the different peaks with experimental data is achieved, but the overall spectra are slightly displaced because of solvent effects. [source] Effect of the Complexant Shape on the Large First Hyperpolarizability of Alkalides Li+(NH3)4M,,CHEMPHYSCHEM, Issue 8 2006Ying-Qi Jing Abstract The effect of complexant shape effect on the first hyperpolarizability ,0 of alkalides Li+(NH3)4M, (M=Li, Na, K) was explored. At the MP2/6-311++G level, Li+(NH3)4M, (M=Li, Na, K) have considerable ,0 values due to excess electrons from chemical doping and charge transfer. By comparison with the alkalides Li+(calix[4]pyrrole)M,, a complexant shape effect in Li+(NH3)4M, is detected. The ,0 values of Li+(NH3)4M, with the "smaller", inorganic, Td -symmetric (NH3)4 complexant are more than four times larger than those of Li+(calix[4]pyrrole)M, with the "larger", organic C4v -symmetric calix[4]pyrrole complexant. The ratios of the ,0 values of Li+(NH3)4M, and Li+(calix[4]pyrrole)M, are 6.57 (M=Li,), 6.55 (M=Na), and 5.17 (M=K). In the Li+(NH3)4M, systems, the NBO charge and oscillator strength are found to monotonically depend on the atomic number of the alkali metal anion. The order of the NBO charges of the alkali anions M, is ,0.667 (M=Li,)>,0.644 (M=Na)>,0.514 (M=K), while the order of the oscillator strengths in the crucial transition is 0.351 (M=Li,)<0.360 (M=Na)<0.467 (M=K). This indicates that complexant shape effects are strong, and consequently the ,0 values of Li+(NH3)4M, are found to be ,0=70,295 (M=Li,)<96,780 (M=Na)<185,805 a.u. (M=K). This work reveals that the use of a high-symmetry complexant is an important factor that should be taken into account when enhancing the first hyperpolarizability of alkalides by chemical doping. [source] | |||||||||||||