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2,4,6-trichloroanisole and 2,4,6-tribromoanisole were investigated by means of electron transmission spectroscopy and two different types of dissociative electron attachment spectrometers. The results obtained were interpreted with the support of density functional theory calculations. The dominant dissociative decay channels of the temporary molecular negative ions lead to the formation of Cl- and Br-in the low electron energy region. Formation of long-lived parent anions is observed at thermal electron energies. Their relative intensity depends on the experimental time window, ∼36 μs in the case of the static magnet mass analyzer and ∼200 μs for the quadrupole mass analyzer employed. The results obtained may be useful for rapid detection of these compounds in wine and pharmaceutical industries, as well as other branches connected to the food industry, e.g., packaging. [ABSTRACT FROM AUTHOR]

Herein, terahertz (THz) time domain spectroscopy is used to measure the complex conductivity of semi-insulating CoFe2O4 nanoparticles (NPs) and nano-hollow spheres (NHSs) with different diameters ranging from 100 to 350 nm having a nanocrystalline shell thickness of 19 to 90 nm, respectively. Interestingly, the magnitude of conductivity for CoFe2O4 NPs and NHSs of same average diameter (∼100 nm) for a given frequency of 0.3 THz is found to be 0.33 S/m and 9.08 S/m, respectively, indicating that the hollow structure exhibits greater THz conduction in comparison to its solid counterpart. Moreover, THz conductivity can be tailored by varying the nano-shell thickness of NHSs, and a maximum conductivity of 15.61 S/m is observed at 0.3 THz for NHSs of average diameter 250 nm. A detailed study reveals that thermally activated polaronic hopping plays the key role in determining the electrical transport property of CoFe2O4 nanostructures, which is found to solely depend on their magnitude of THz absorptivity. The non-Drude conductivity of all CoFe2O4 nanostructures is well described by the Polaron model instead of the Drude-Smith model, which is relevant for backscattering of free electrons in a nanostructured material. The Polaron model includes intra-particle and interparticle polaronic conductivities for closely spaced magnetic nanostructures and provides a mean free path of 29nm for CoFe2O4 NPs of diameter 100nm, which is comparable with its average crystallite size, indicating the applicability of the developed model for nanomaterials where charge transport is determined by polaronic hopping. Finally, we have demonstrated the morphology and size dependent magnetic measurements of ferrimagnetically aligned CoFe2O4 nanostructures through a vibrating sample magnetometer in the temperature range of 80-250 K, revealing that the disordered surface spin layer of nanostructures significantly controls their magnetism. [ABSTRACT FROM AUTHOR]

The electron g factor in an ensemble of InAs/InP quantum dots with emission wavelengths around 1.4 μm is measured using time-resolved pump-probe Faraday rotation spectroscopy in different magnetic field orientations. Thereby, we can extend recent single dot photoluminescence measurements significantly towards lower optical transition energies through 0.86 eV. This allows us to obtain detailed insight into the dispersion of the recently discovered g factor anisotropy in these infrared emitting quantum dots. We find with decreasing transition energy over a range of 50 meV a strong enhancement of the g factor difference between magnetic field normal and along the dot growth axis, namely, from 1 to 1.7. We argue that the g factor cannot be solely determined by the confinement energy, but the dot asymmetry underlying this anisotropy therefore has to increase with increasing dot size. [ABSTRACT FROM AUTHOR]

Pyrolytic dissociation of Cl2 is employed to dope helium droplets with single Cl atoms. Sequential addition of NH3 to Cl-doped droplets leads to the formation of a complex residing in the entry valley to the substitution reaction Cl + NH3 → ClNH2 + H. Infrared Stark spectroscopy in the NH stretching region reveals symmetric and antisymmetric vibrations of a C3v symmetric top. Frequency shifts from NH3 and dipole moment measurements are consistent with a ClNH3 complex containing a relatively strong two-center three-electron (2c-3e) bond. The nature of the 2c-3e bonding in ClNH3 is explored computationally and found to be consistent with the complexation-induced blue shifts observed experimentally. Computations of interconversion pathways reveal nearly barrierless routes to the formation of this complex, consistent with the absence in experimental spectra of two other complexes, NH3Cl and Cl-HNH2, which are predicted in the entry valley to the hydrogen abstraction reaction Cl + NH3 → HCl + NH2. [ABSTRACT FROM AUTHOR]

The temperature dependence of the electron Landé g-factor in bulk cubic GaN is investigated over an extremely broad temperature range from 15K up to 500K by time-resolved Kerr-rotation spectroscopy. The g-factor is found to be approximately constant over the full investigated temperature range. Calculations by k · p-theory predict a negligible temperature dependence g(T) in complete agreement with the experiment as a consequence of the large band-gap and small spin orbit splitting in cubic GaN. [ABSTRACT FROM AUTHOR]

The effect of hole transport on the performance of infrared light emitting diodes (LED) was investigated. The active area of the LEDs comprised two type-II superlattices with different periods and widths connected in series. Electroluminescence spectra of the devices with different positions of long wave and mid wave superlattice sections were mostly contributed by the superlattice closest to the p-contact. The experimental results indicate that due to suppressed vertical hole transport, the recombination of electrically injected electrons and holes in a type II superlattice LED active region takes place within a few superlattice periods near p-barrier. Possible reason for the effect is reduction of hole diffusion coefficient in an active area of a superlattice LED under bias. [ABSTRACT FROM AUTHOR]

Electrical properties and deep electron and hole traps spectra are compared for undoped n-GaN films grown by hydride vapor phase epitaxy (HVPE) in the regular process (standard HVPE samples) and in HVPE process optimized for decreasing the concentration of residual donor impurities (improved HVPE samples). It is shown that the residual donor density can be reduced by optimization from ∼1017 cm-3 to (2-5)×1014 cm-3. The density of deep hole traps and deep electron traps decreases with decreased donor density, so that the concentration of deep hole traps in the improved samples is reduced to ∼5×1013 cm-3 versus 2.9×1016 cm-3 in the standard samples, with a similar decrease in the electron traps concentration. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the optical properties of confined electronic states in ultra-thin Al0.27Ga0.73As/GaAs/vacuum surface quantum wells by using photoreflectance spectroscopy at room temperature. Well-resolved doublet structures were found in the spectra. The energy of the features increases with decreasing well width in agreement with the predictions of a model of the transition energy between confined electron and hole states in a surface quantum well. Both the transition broadening and intensity behaviors are also well explained by the effective mass approximation theory. The offset between the un-perturbed theoretical transition energy and the experimental data has been explained by surface-state interaction effects. Moreover, the fact that the light hole ground state in the surface quantum well can be pushed out from the surface quantum well has been directly observed experimentally. [ABSTRACT FROM AUTHOR]

A general theory of electronic excitations in aggregates of molecules coupled to intramolecular vibrations and the harmonic environment is developed for simulation of the third-order nonlinear spectroscopy signals. It is applied in studies of the time-resolved two-dimensional coherent spectra of four characteristic model systems: weakly/strongly vibronically coupled molecular dimers interacting with high/low frequency intramolecular vibrations. The results allow us to (i) classify and define the typical spectroscopic features of vibronically coupled molecules, (ii) separate the cases, when the long-lived quantum coherences due to vibrational lifetime borrowing should be expected, (iii) define when the complete exciton-vibrational mixing occurs, and (iv) when separation of excitonic and vibrational coherences is possible. [ABSTRACT FROM AUTHOR]

Transitions in atoms and molecules provide an ideal test ground for constraining or detecting a possible variation of the fundamental constants of nature. In this perspective, we review molecular species that are of specific interest in the search for a drifting proton-to-electron mass ratio µ. In particular, we outline the procedures that are used to calculate the sensitivity coefficients for transitions in these molecules and discuss current searches. These methods have led to a rate of change in µ bounded to 6 × 10-14/yr from a laboratory experiment performed in the present epoch. On a cosmological time scale, the variation is limited to |Δµ/µ| < 10-5 for look-back times of 10-12 × 109 years and to |Δµ/µ| < 10-7 for look-back times of 7× 109 years. The last result, obtained from high-redshift observation of methanol, translates into µ/µ = (1.4 ± 1.4) × 10-17/yr if a linear rate of change is assumed. [ABSTRACT FROM AUTHOR]

We have developed a new approach to the computation of third-order spectroscopic signals of molecular rings, by incorporating the Davydov soliton theory into the nonlinear response function formalism. The Davydov D1 and D Ansätze have been employed to treat the interactions between the excitons and the primary phonons, allowing for a full description of arbitrary exciton-phonon coupling strengths. As an illustration, we have simulated a series of optical 2D spectra for two models of molecular rings. [ABSTRACT FROM AUTHOR]

Potential energy curves have been constructed using coupled cluster with singles, doubles, and perturbative triple excitations (CCSD(T)) in combination with all-electron and pseudopotential-based multiply augmented correlation consistent basis sets [m-aug-cc-pV(n + d)Z; m = singly, doubly, triply, n = D,T,Q,5]. The effect of basis set superposition error on the spectroscopic properties of Ar-Zn, Ar2-Zn, Ar-Ag+, and Ar2-Ag+ van der Waals complexes was examined. The diffuse functions of the doubly and triply augmented basis sets have been constructed using the even-tempered expansion. The a posteriori counterpoise scheme of Boys and Bernardi and its generalized variant by Valiron and Mayer has been utilized to correct for basis set superposition error (BSSE) in the calculated spectroscopic properties for diatomic and triatomic species. It is found that even at the extrapolated complete basis set limit for the energetic properties, the pseudopotential-based calculations still suffer from significant BSSE effects unlike the all-electron basis sets. This indicates that the quality of the approximations used in the design of pseudopotentials could have major impact on a seemingly valence-exclusive effect like BSSE. We confirm the experimentally determined equilibrium internuclear distance (re), binding energy (De), harmonic vibrational frequency (ωe), and C1Π ← X1Σ transition energy for ArZn and also predict the spectroscopic properties for the low-lying excited states of linear Ar2-Zn (X1Σg, 3Πg, 1Πg), Ar-Ag+ (X1Σ, 3Σ, 3Π, 3Δ, 1Σ, 1Π, 1Δ), and Ar2-Ag+ (X1Σg, 3Σg, 3Πg, 3Δg, 1Σg, 1Πg, 1Δg) complexes, using the CCSD(T) and MR-CISD + Q methods, to aid in their experimental characterizations. [ABSTRACT FROM AUTHOR]

We report in-plane Cu-O atomic displacements as a function of doping in the La2-xSrxCuO4 system, determined by polarized Cu K-edge extended x-ray absorption fine structure measurements. We find a wide distribution of the Cu-O bonds showing a single peak asymmetric function for the system at low doping, which gets two peak function for the underdoped and optimally doped superconducting phases before turning to a single peak function for the overdoped phase. The results provide a direct evidence of critical local lattice fluctuations for an optimum transition temperature in the superconducting phases hosting quantum stripes. [ABSTRACT FROM AUTHOR]

We study the localization of dressed Dirac electrons in a cylindrical quantum dot (QD) formed on monolayer and bilayer graphene by spatially different potential profiles. Short lived excitonic states which are too broad to be resolved in linear spectroscopy are revealed by cross peaks in the photon-echo nonlinear technique. Signatures of the dynamic gap in the two-dimensional spectra are discussed. The effect of the Coulomb induced exciton-exciton scattering and the formation of biexciton molecules are demonstrated. [ABSTRACT FROM AUTHOR]

Based entirely upon actual experimental observations on electron-phonon coupling, we develop a theoretical framework to show that the lowest energy band of the Fenna-Matthews-Olson complex exhibits observable features due to the quantum nature of the vibrational manifolds present in its chromophores. The study of linear spectra provides us with the basis to understand the dynamical features arising from the vibronic structure in nonlinear spectra in a progressive fashion, starting from a microscopic model to finally performing an inhomogeneous average. We show that the discreteness of the vibronic structure can be witnessed by probing the diagonal peaks of the nonlinear spectra by means of a relative phase shift in the waiting time resolved signal. Moreover, we demonstrate that the photon-echo and non-rephasing paths are sensitive to different harmonics in the vibrational manifold when static disorder is taken into account. Supported by analytical and numerical calculations, we show that non-diagonal resonances in the 2D spectra in the waiting time, further capture the discreteness of vibrations through a modulation of the amplitude without any effect in the signal intrinsic frequency. This fact generates a signal that is highly sensitive to correlations in the static disorder of the excitonic energy albeit protected against dephasing due to inhomogeneities of the vibrational ensemble. [ABSTRACT FROM AUTHOR]

Angle-resolved metastable fragments yields spectra have been measured in the N 1s ionization region of the N2 and C 1s ionization region of CO. These spectra are compared with zero kinetic energy electron and photoelectron spectra. It has been shown that an isotropic metastable fragments yields spectra are almost identical with the ZEKE spectrum, whereas metastable fragments yields spectra with the Σ-Σ transition show similarity with photoelectron spectra. This means that these spectra clearly contain information about two shake-up mechanisms: conjugate and direct shake-up processes. All the peaks in the metastable photofragment spectra can be assigned as either satellite states or double/triple excitation states. Thus, it was shown that angle-resolved metastable photofragment spectroscopy could be used to help characterize multi-electron excitation states in general. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) of Mn2+ and Fe3+ ions has been used as a probe of local static and dynamic lattice distortions in the relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN) and solid solutions (1-x)PbMg1/3Nb2/3O3 - xPbTiO3 (x = 0.075-0.33) at temperatures from 290 to 800 K. We have found that the spectrum of the both ions in PMN contains two components: One component corresponds to the resonances from the lattice regions where the perovskite cubic structure is distorted statically while the second component corresponds to the regions where ionic displacements undergo significant dynamic fluctuations. The EPR spectrum from these lattice regions shows the motional narrowing behavior at 350-500 K. We assign these regions with reorientable polar nanoregions responsible for the dielectric relaxation in PMN. From the motional narrowing of the spectral lines, we have determined parameters of the Vogel--Fulcher law describing the rate of ionic hopping between symmetrically equivalent off-center positions. These parameters (Ea = 840-880 K, τ0 ∼ 10-13 s, Tg = 220 K) are in a satisfactory agreement with those reported for the dielectric relaxation. The fraction of polar nanoregions in PMN determined from the EPR intensity is about 20% to 30%. An addition of PbTiO3 to PMN decreases total volume of the polar nanoregions and also suppresses their reorientational dynamics. The EPR spectra do not change in the temperature range from 500 to 800 K, including the temperatures far above the Burns temperature 620 K. [ABSTRACT FROM AUTHOR]

Effects of Fe doping on the structural, optical and magnetic properties of sol-gel derived Zn1-xFexO (0 ≤ x ≤ 0.06) nanoparticles have been investigated. The single-phased wurtzite structure has been characterized by XRD analysis. The nanocrystalline nature of the samples and their crystallinity has been confirmed by TEM measurements. Raman spectroscopy has been employed to study the crystalline quality and structural disorders. FTIR analysis confirms the wurtzite structure and formation of tetrahedral coordination of the oxygen ions surrounding the zinc ions. UV-Vis measurements show that the band gap is fast blue shifted in lower Fe-concentrations and after that slowly red shifted in higher Fe-concentrations. This may be attributed to the Burstein-Moss effect which is prevailed throughout the range of Fe-doping and sp-d exchange interaction that plays a role in higher Fe-concentration. Magnetic hysteresis measurement (M-H) shows that Zn0.96Fe0.04O exhibits ferromagnetic behavior at room temperature. [ABSTRACT FROM AUTHOR]

The second-order algebraic construction (ADC(2)) approach to the two-particle (pp) propagator, devised to compute double ionization energies and associated spectroscopic amplitudes, is reformulated and extended using the concept of intermediate state representations (ISR). The ISR formulation allows one to go beyond the general limitations inherent to the propagator approach, as here (N-2)-electron wave functions and properties become directly accessible. The (N-2)-electron ISR(2) equations for a general one-particle operator have been derived and implemented in a recent version of the double ionization ADC(2) program. As a first test of the method, the dipole moments of a series of 2h states of LiH, HF, and H2O were computed and compared to the results of a full configuration interaction (FCI) treatment. The dipole moments obtained at the ADC(2)/ISR(2) computational level are in good agreement with the FCI results. [ABSTRACT FROM AUTHOR]

The magnetoplasmon spectrum of two-dimensional electron gas systems with both Rashba and Dresselhaus spin-orbit interactions is investigated theoretically. The coexistence of the two types of spin-orbit interactions leads to resonant splittings of the collective excitation modes and makes the magnetoplasmon spectrum anisotropic with respect to the direction of the wave vector. The anticrossing gaps in the magnetoplasmon spectrum vary with the angle of the wave vector and reach their extrema at several fixed directions. Such anisotropic splittings could be used to evaluate the relative strength of the Rashba and Dresselhaus spin-orbit interactions in two-dimensional electron systems. [ABSTRACT FROM AUTHOR]

In this work we present the spectroscopic properties of KY3F10 (KY3F) single crystals activated with thulium and co-doped with ytterbium and neodymium ions. The most important processes that lead to the thulium up-conversion emissions in the blue and ultraviolet regions were identified. A time-resolved luminescence spectroscopy technique was employed to measure the luminescence decays and to determine the most important mechanisms involved in the up-conversion process that populates 1G4 and 1D2 (Tm3+) excited states. Analysis of the energy-transfer processes dynamics using selective pulsed-laser excitations in Yb:Tm:Nd, Tm:Nd, and Tm:Yb KY3F crystals show that the energy transfer from Nd3+ to Yb3+ ions is the mechanism responsible for the enhancement of the blue up-conversion efficiency in the Yb:Tm:Nd:KY3F when compared with the Yb:Tm system. A study of the energy transfer processes in Yb:Tm:Nd:KY3F crystal showed that the 1G4 excited level is mainly populated by a sequence of two nonradiative energy transfers that starts well after the Nd3+ and Tm3+ excitation at 797 nm according to: Nd3+ (4F3/2) → Yb3+ (2F7/2) followed by Yb3+ (2F5/2) → Tm (3H4) → Tm3+ (1G4). Results of numerical simulation of the rate equations system showed that a population inversion for 483.1 nm laser emission line is attained for a pumping rate threshold of 98 s-1, which is equivalent to an intensity of 3.3 KW cm-2 for a continuous laser pumping at 797 nm for Yb(30 mol%):Tm(0.5 mol%):Nd(1 mol%):KY3F. Nevertheless, best Yb3+ concentration for the laser emission near 483.1 nm was estimated to be within 40 and 50 mol%. On the other hand, a population inversion was not observed for the case of 960 nm (Yb3+) pumping. [ABSTRACT FROM AUTHOR]

The Lanczos algorithm (LA) is a useful iterative method for the reduction of a large matrix to tridiagonal form. It is a storage efficient procedure requiring only the preceding two Lanczos vectors to compute the next. The quasi-minimal residual (QMR) method is a powerful method for the solution of linear equation systems, Ax = b. In this report we provide another application of the QMR method: we incorporate QMR into the LA to monitor the convergence of the Lanczos projections in the reduction of large sparse matrices. We demonstrate that the combined approach of the LA and QMR can be utilized efficiently for the orthogonal transformation of large, but sparse, complex, symmetric matrices, such as are encountered in the simulation of slow-motional 1D- and 2D-electron spin resonance (ESR) spectra. Especially in the 2D-ESR simulations, it is essential that we store all of the Lanczos vectors obtained in the course of the LA recursions and maintain their orthogonality. In the LA-QMR application, the QMR weight matrix mitigates the problem that the Lanczos vectors lose orthogonality after many LA projections. This enables substantially more Lanczos projections, as required to achieve convergence for the more challenging ESR simulations. It, therefore, provides better accuracy for the eigenvectors and the eigenvalues of the large sparse matrices originating in 2D-ESR simulations than does the previously employed method, which is a combined approach of the LA and the conjugate-gradient (CG) methods, as evidenced by the quality and convergence of the 2D-ESR simulations. Our results show that very slow-motional 2D-ESR spectra at W-band (95 GHz) can be reliably simulated using the LA-QMR method, whereas the LA-CG consistently fails. The improvements due to the LA-QMR are of critical importance in enabling the simulation of high-frequency 2D-ESR spectra, which are characterized by their very high resolution to molecular orientation. [ABSTRACT FROM AUTHOR]

Anionic tetrahydrofuran clusters (THF)n- (1≤n≤100) are studied with photoelectron imaging as gas-phase precursors for electrons solvated in THF. Photoelectron spectra of clusters up to n=5 show two peaks, one of which is attributed to a solvated open chain radical anion and the other to the closed THF ring. At n=6, the spectra change shape abruptly, which become more characteristic of (THF)n- clusters containing solvated electrons. From n=6-100, the vertical detachment energies (VDEs) of these solvated electron clusters increase from 1.96 to 2.71 eV, scaling linearly with n-1/3. For fully deuterated (THF-d8)n- clusters, the apparent transition to a solvated electron cluster is delayed to n=11. Extrapolation of the VDEs to infinite cluster size yields a value of 3.10 eV for the bulk photoelectric threshold. The relatively large VDEs at onset and small stabilization with increasing cluster size compared to other solvated electron clusters may reflect the tendency of the bulk solvent to form preexisting voids that can readily solvate a free electron. [ABSTRACT FROM AUTHOR]

Restricted-spin coupled-cluster single-double plus perturbative triple excitation {RCCSD(T)} calculations were carried out on the X 2B1 and A 2A1 states of AsH2 employing the fully relativistic small-core effective core potential (ECP10MDF) for As and basis sets of up to the augmented correlation-consistent polarized valence quintuple-zeta (aug-cc-pV5Z) quality. Minimum-energy geometrical parameters and relative electronic energies were evaluated, including contributions from extrapolation to the complete basis set limit and from outer core correlation of the As 3d10 electrons employing additional tight 4d3f2g2h functions designed for As. In addition, simplified, explicitly correlated CCSD(T)-F12 calculations were also performed employing different atomic orbital basis sets of up to aug-cc-pVQZ quality, and associated complementary auxiliary and density-fitting basis sets. The best theoretical estimate of the relative electronic energy of the A 2A1 state of AsH2 relative to the X 2B1 state including zero-point energy correction (T0) is 19 954(32) cm-1, which agrees very well with available experimental T0 values of 19 909.4531(18) and 19 909.4910(17) cm-1 obtained from recent laser induced fluorescence and cavity ringdown absorption spectroscopic studies. In addition, potential energy functions (PEFs) of the X 2B1 and A 2A1 states of AsH2 were computed at different RCCSD(T) and CCSD(T)-F12 levels. These PEFs were used in variational calculations of anharmonic vibrational wave functions, which were then utilized to calculate Franck–Condon factors (FCFs) between these two states, using a method which includes allowance for anharmonicity and Duschinsky rotation. The A(0,0,0)-X single vibronic level (SVL) emission spectrum of AsH2 was simulated using these computed FCFs. Comparison between simulated and available experimental vibrationally resolved spectra of the A(0,0,0)-X SVL emission of AsH2, which consist essentially of the bending (2n) series, suggests that there is a significant loss in intensity in the low emission energy region of the experimental spectrum. [ABSTRACT FROM AUTHOR]

Parity violation (PV) effects to the electronic ground state structure for a series of chiral tungsten molecules of the type NWXYZ (X, Y, Z=H, F, Cl, Br, or I) are compared using four- (Dirac) and two- (X2C) component relativistic Hartree–Fock and density functional theories. The results show the computationally more affordable two-component X2C approach yields accurate results for all molecules investigated. The PV energy differences between the two enantiomers range from as little as 0.4 Hz for NWClBrI to 140 Hz for NWHClI using a generalized gradient approximation including exact exchange (B3LYP). The W[Single_Bond]N stretching mode in these molecules lies in the experimentally favorable CO2 laser frequency range, and we therefore investigated PV effects in vibrational transitions using a single normal mode analysis. Here the PV frequency shift between the two enantiomers ranges from 1.6 mHz for NWFBrI to 710 mHz for NWHClI. Thus these types of molecules could be useful for the future detection of PV effects in chiral molecules. [ABSTRACT FROM AUTHOR]

It has been found that 2,4,6 trinitrotoluene (TNT) displays a 420 nm peak in differential reflection spectrometry spectra. Differential reflection spectrometry uses UV and visible light to measure the photon energy absorbed by electrons when they move to a higher energy state. This particular optical feature for TNT has been previously reported by the authors. The physical origin of the described feature is investigated using computational chemistry. Through this molecular modeling, circumstances where the 420 nm feature may occur have been isolated. In addition, the participating molecular orbitals have been suggested from these calculations as in the nitro groups and the ring carbon bonded to this group. [ABSTRACT FROM AUTHOR]

The Ã-X electronic absorption spectrum of vinoxy radical has been investigated using room temperature cavity ringdown spectroscopy. Analysis of the observed bands on the basis of computed vibrational frequencies and rotational envelopes reveals that two distinct types of features are present with comparable intensities. The first type corresponds to “normal” allowed electronic transitions to the origin and symmetric vibrations in the à state. The second type is interpreted in terms of excitations to asymmetric à state vibrations, which are only vibronically allowed by Herzberg–Teller coupling to the B state. Results of electronic structure calculations indicate that the magnitude of the Herzberg–Teller coupling is appropriate to produce vibronically induced transitions with intensities comparable to those of the normal bands. [ABSTRACT FROM AUTHOR]

The expansion dynamics of ion and neutral species in laterally colliding laser produced aluminum plasmas have been investigated using time and space resolved optical emission spectroscopies and spectrally and angularly resolved fast imaging. The emission results highlight a difference in neutral atom and ion distributions in the stagnation layer where, at a time delay of 80 ns, the neutral atoms are localized in the vicinity of the target surface (<1 mm from the target surface) while singly and doubly charged ions lie predominantly at larger distances, <1.5 and <2 mm, respectively. The imaging results show that the ions were found to form a well defined, but compressed, stagnation layer at the collision front between the two seed plasmas at early times (Δt<80 ns). On the other hand, the excited neutrals were observed to form a V-shaped emission feature at the outer regions of the collision front with enhanced neutral emission in the less dense, cooler regions of the stagnation layer. [ABSTRACT FROM AUTHOR]

We report a systematic measurement of the space charge effect observed in the few-picosecond laser pulse regime in laser-based solid-state photoemission spectroscopy experiments. The broadening and the shift of a gold Fermi edge as a function of spot size, laser power, and emission angle are characterized for pulse lengths of 6 ps and 6 eV photon energy. The results are used as a benchmark for an N-body numerical simulation and are compared to different regimes used in photoemission spectroscopy. These results provide an important reference for the design of time- and angle-resolved photoemission spectroscopy setups and next-generation light sources. [ABSTRACT FROM AUTHOR]

Distributions of emission intensity from radicals, electron temperature, and rotational temperature at a radio frequency of 27.12 MHz plasma in water are clarified by detailed spectroscopy measurement. Through this investigation, the following were observed. The points of maximum emission intensity of Hα, Hβ, O (777 nm), and O (845 nm) are almost the same, while that of OH shifts upward. The electron temperature decreases, while the rotational temperature increases with pressure. The distribution of the electron temperature changes at a threshold pressure, which is concerned with a change in the electron discharge mechanism. The self-bias of the electrode changes from a negative to positive at a threshold pressure. The point of the maximum rotational temperature of OH radicals shifts to approximately 1 mm above that for the maximum intensity of OH emission. [ABSTRACT FROM AUTHOR]

Ho3+-doped and Ho3+/Yb3+-codoped lead bismuth gallate (PBG) oxide glasses were prepared and their spectroscopic properties were investigated. The derived Judd–Ofelt intensity parameters (Ω2=6.81×10-20 cm2, Ω4=2.31×10-20 cm2, and Ω6=0.67×10-20 cm2) indicate a higher asymmetry and stronger covalent environment for Ho3+ sites in PBG glass compared with those in tellurite, fluoride (ZBLAN), and some other lead-contained glasses. Intense frequency upconversion emissions peaking at 547, 662, and 756 nm as well as infrared emissions at 1.20 and 2.05 μm in Ho3+/Yb3+-codoped PBG glass were observed, confirming that energy transfer between Yb3+ and Ho3+ takes place, and a two-phonon-assisted energy transfer from Yb3+ to Ho3+ ions was determined by the calculation using phonon sideband theory. The 1.20 μm emission observed was primarily due to the weak multiphonon deexcitation originated from the small phonon energy of PBG glass (∼535 cm-1). A large product of emission cross-section and measured lifetime (9.93×10-25 cm2 s) was obtained for the 1.20 μm emission and the gain coefficient dependence on wavelength with population inversion rate (P) was performed. The peak emission cross-section for 2.05 μm emission was calculated to be 4.75×10-21 cm2. The relative mechanism of Ho3+-doped and Ho3+/Yb3+-codoped PBG glasses on their spectroscopic properties was also discussed. Our results suggest that Ho3+/Yb3+-doped PBG glasses are a good potential candidate for the frequency upconversion devices and infrared amplifiers/lasers. [ABSTRACT FROM AUTHOR]

This work aims specifically at studying the evolution of point defects induced by electron irradiation in the cubic polytype of SiC (3C-SiC) at temperatures ranging from 10 to 1450 K by means of photoluminescence (PL) spectroscopy. We identified a first annealing stage between 200 and 245 K, which probably results from migration of interstitials in the carbon sublattice. Moreover, we confirmed the high thermal stability of defect-related PL signals up to about 1100 K and calculated the activation energies associated with their annihilation. Finally, we studied the effect of a high temperature treatment at 1400 K on the DI center PL intensity in a single-crystal sample irradiated by electrons below the threshold displacement energy of the silicon sublattice. This allows checking the relevance of recent defect models based upon the migration of atoms in the carbon sublattice during the irradiation process. We conclude that the DI center does not involve the silicon vacancy and could be assigned to an isolated silicon antisite SiC. [ABSTRACT FROM AUTHOR]

We have performed systematic studies of wurtzite GaN/AlN quantum dots grown on polar and nonpolar surfaces. For this purpose, experimentally observed quantum dot geometries have been employed within an eight-band k·p model. The spatial separation of electrons and holes due to polarization potentials is found to be much larger in nonpolar than in polar grown quantum dots. In order to improve the electron-hole overlap and thus the recombination rates, we have varied the shape, size, and the periodic arrangement of nonpolar quantum dots. We observed the strongest improvement of the charge carrier overlap in nonpolar quantum dots that have a reduced dimension. If the size is reduced below 60% of the dimensions reported recently in literature, this increase is clearly more pronounced than for the polar quantum dots, indicating much better recombination rates in smaller nonpolar quantum dots. [ABSTRACT FROM AUTHOR]

An electronic excitation spectrum of the B–X transition of the CH2CHS (vinylthio, thiovinoxy) radical was observed in the range of 21 800–23 400 cm-1 by fluorescence depletion spectroscopy. Vibrational assignments for the depletion spectrum were made with the help of a theoretical excitation spectrum computed from results of ab initio calculations. The previously observed emission spectrum [M. Nakajima et al., J. Chem. Phys. 126, 044307 (2007)] was also reassigned based on the present theoretical study. Rotational band contours observed in the depletion spectrum show a large variation due to a vibrational-level dependence of the excited state lifetime. However, no obvious vibrational mode dependence of the lifetime was observed. [ABSTRACT FROM AUTHOR]

The effect of diffuse electron density at the boundary surfaces of Au-core Ag-shell bimetallic nanospheres on their optical properties such as extinction spectra is investigated by considering a multiple shell model for both the interfaces consisting of exponentially decreasing electron density profiles corresponding to a minimized energy density functional. The dielectric constants for the shells of varying electron density have been obtained by proposing a new simple approach. The diffuseness of the electron density at the boundary surfaces is found to give rise to peak broadening to some extent and also seems to favor the experimental spectra. [ABSTRACT FROM AUTHOR]

A simulation formalism for the nonlinear response of vibrational excitons is presented and applied to the OH stretching vibrations of neat liquid H2O. The method employs numerical integration of the Schrödinger equation and allows explicit treatment of fluctuating transition frequencies, vibrational couplings, dipole moments, and the anharmonicities of all these quantities, as well as nonadiabatic effects. The split operator technique greatly increases computational feasibility and performance. The electrostatic map for the OH stretching vibrations in liquid water employed in our previous study [A. Paarmann et al., J. Chem. Phys. 128, 191103 (2008)] is presented. The two-dimensional spectra are in close agreement with experiment. The fast 100 fs dynamics are primarily attributed to intramolecular mixing between states in the two-dimensional OH stretching potential. Small intermolecular couplings are sufficient to reproduce the experimental energy transfer time scales. Interference effects between Liouville pathways in excitonic systems and their impact on the analysis of the nonlinear response are discussed. [ABSTRACT FROM AUTHOR]

The time dependent dielectric breakdown in Co–Fe–B/MgO/Co–Fe–B magnetic tunnel junctions was investigated by voltage ramp experiments. The measurements were done for two types of junctions: one set of junctions had exchange biased (pinned) bottom electrodes and one set had exchange biased (pinned) top electrodes with an additional artificial ferrimagnet. We found a significant polarity dependence in the dielectric breakdown: top as well as bottom pinned tunnel junctions showed higher breakdown voltage when the top electrode was biased positively compared to negative bias. In contrast to this the differential resistance (dV/dI)-V spectra revealed an asymmetry for the top pinned junctions which was reversed in comparison to the bottom pinned system. This indicates that both asymmetries have different origins. Additionally the bottom pinned junctions showed in general slightly lower breakdown voltages and stronger magnon excitation in the inelastic electron tunneling (d2I/dV2)-V spectra than the top pinned junctions. Possible reasons for these correlations are discussed. [ABSTRACT FROM AUTHOR]

A series of bound exciton transitions of a bulk ZnO sample has been studied by high resolution magnetophotoluminescence spectra. Ten sharp intense bound exciton emissions are classified into three groups according to their dependences on magnetic field, angle, and circular polarization of the emission lines. The charge states of the defect centers and exciton types are identified. The effective g factors of the electrons and holes are determined. [ABSTRACT FROM AUTHOR]

Phonon-plasmon coupled mode Raman spectra of n-type GaSb were measured at room temperature as a function of electron concentration. These spectra were obtained using an optical system based on 752.55 nm excitation. Utilization of this wavelength permits greater sensitivity to GaSb coupled mode Raman scattering over a wider doping range than is possible with visible wavelength excitation-based systems. A relatively simple spectral model for the electronic contribution to the dielectric function was evaluated for determination of electron concentration from the bulk coupled mode spectra. The electron concentrations were determined from the Raman spectra by minimizing the sum of the squared residuals between a measured and a simulated spectrum as a function of Fermi energy and a plasmon damping parameter. The electron concentrations determined from the fits to the Raman spectra were compared to the electron concentrations determined from single magnetic field Hall effect measurements that were corrected to account for carriers in two conduction band minima. The electron concentrations determined using the two methods differed from ≈-16% at low doping levels to ≈+24% at high doping levels. In general, compared to the electron concentrations determined from the corrected Hall effect measurements, the electron concentrations determined from the Raman spectra were lower for epilayers with lower Hall effect electron concentrations and higher for epilayers with higher Hall effect electron concentrations. The deviations between the results obtained with the two methods were attributed to the impact of uncertainties in GaSb material properties on the accuracy of the correction to the single field Hall effect measurements and to the limitations of the spectral model employed. [ABSTRACT FROM AUTHOR]

Photo- and thermoluminescence (TL) spectra of NaLaF4:Ln3+ (Ln=Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm) and NaLaF4:Ce3+, Ln3+ (Ln=Nd,Sm,Ho,Er,Tm) are presented and used together with the empirical Dorenbos model in order to establish the 4f energy level positions of all tri- and divalent lanthanide ions doped in NaLaF4. The information will be presented in the form of an energy level diagram. It is shown that in addition to this diagram only two assumptions, viz., the presence of two host related electron traps and the presence of Vk-centers, are necessary for explaining the lanthanide-specific TL glow curves of both Ln mono- and Ce–Ln codoped NaLaF4. [ABSTRACT FROM AUTHOR]

The origin of annealing-induced variations in the effective work function of Ta-based conductors (TaC, Ta2C, and TaNx) at interfaces with SiO2 and HfO2 dielectrics is investigated using the spectroscopy of internal photoemission (IPE) of electrons. Two physical mechanisms were considered that could affect the Ta-based metal/oxide barrier: (a) oxidation of the metal conductor after thermal treatment by oxygen supplied from the oxide layer, resulting in a variation in the density of electron states inside the metal emitter, and (b) annealing-induced variations in the barrier at the interface. Field-dependent and differential IPE experiments allowed us to identify the latter as the dominant mechanism causing the barrier instability after thermal treatment in nonoxidizing ambient. The incorporation of negatively charged centers in the near-interface oxide layers is the most likely explanation for the significant increase (∼0.6 eV) of the barrier height after annealing, leading us to the hypothesis that Ta may diffuse into the oxide layer, and thereby be at the origin of the negative charge creation. [ABSTRACT FROM AUTHOR]

The optical absorption spectra of the hydrated electron (eaq-) in supercritical (heavy) water (SCW) are measured by electron pulse radiolysis techniques as a function of water density at three temperatures of 380, 390, and 400 °C, and over the density range of ∼0.2–0.65 g/cm3. In agreement with previous work, the position of the eaq- absorption maximum (EAmax) is found to shift slightly to lower energies (spectral “redshift”) with decreasing density. A comparison of the present EAmax-density data with other measurements already reported in the literature in subcritical (350 °C) and supercritical (375 °C) water reveals that at a fixed pressure, EAmax decreases monotonically with increasing temperature in passing through the phase transition at tc. By contrast, at constant density, EAmax exhibits a minimum as the water passes above the critical point into SCW. These behaviors are explained in terms of simple microscopic arguments based on the crucial role played by local density and configurational fluctuations (associated with criticality) in providing pre-existing polymeric clusters, which act as trapping sites for electrons. [ABSTRACT FROM AUTHOR]

This work combines high level ab initio calculations with multidimensional Franck–Condon calculations to refine and augment previous assignments of the lower wavenumber region of the A 1B2←X 1A1 band system of fluorobenzene. The strength of the assignment has been greatly assisted by the use of zero electron kinetic energy spectroscopy in a series of pump-probe experiments where the response of the molecule to selective excitation in specific modes prior to ionization has been studied. The net result of this analysis is the reassignment of 7 of the 12 previously assigned bands in the region below about 1000 cm-1 using a strategy that aims to trace the origins of excited state normal modes of fluorobenzene to the well-known Wilson modes of benzene by taking full account of the Duschinsky mixing that accompanies electronic excitation. Duschinsky normal mode analyses of the ground and first excited states of fluorobenzene as well as the electronic ground state of fluorobenzene cation have shown that the common use of the benzene Wilson notation to describe normal modes of this prototypical benzene derivative is highly questionable, particularly following electronic excitation and ionization. [ABSTRACT FROM AUTHOR]

The infrared (IR) transmission, Raman Scattering, magnetic measurement, and electronic resistance measurement have been carried out in La2-xSrxCu0.94Mn0.06O4 and La2-xSrxCu0.94Ru0.06O4 systems. The superconductivity that is suppressed by impurity reappears as Sr content increases and forms a new relationship of the Meissner volume and Tconset versus Sr doping content. The Mn4+ doping system exhibits twice superconductive phase transitions while Ru4+ doping system exhibits only one superconductive phase transition. Coexistence and competition between superconductivity and magnetism are observed. We suggest that these surprising phenomena should be attributed to the compensation effect that is the electrons on high valence impurities are compensated by holes introduced through Sr doping. This compensation effect is confirmed by our IR spectra results. We also find that the compensation effect is strong for the localized 3d electrons of Mn4+ while very weak for the itinerant 4d electrons of Ru4+. [ABSTRACT FROM AUTHOR]

The relaxation dynamics of solvated electrons from sodium-ammonia-d3 solutions was studied by femtosecond time-resolved near-infrared spectroscopy. The experimental pump-probe data reveal a pulse-width limited pump-induced redshift of the absorption spectrum of the ammoniated electron and a subsequent slower blueshift on a time scale of roughly 200 fs. The spectrotemporal response is interpreted using the nonadiabatic relaxation mechanism for cavity-bound solvated electrons in condensed phases. In particular, we develop a local density-jump model, which traces the dynamic spectrum back to a sequence of a pump-induced cavity expansion due to Pauli repulsion and a succeeding cavity contraction upon nonadiabatic return of the electron back to its ground state. Using the existing thermodynamic data of the solvent and experimental temperature and density-dependent absorption spectra of metal-ammonia solutions, an overall increase in the interparticle distance within the solvent cavity of 25% is crudely estimated. The density-jump model is compared to the temperature-jump model we proposed previously for the femtosecond relaxation dynamics of metal-NH3 solutions. [ABSTRACT FROM AUTHOR]

IR-UV ion-dip spectra of the 7-azaindole (7AI)(CH3OH)n (n=1–3) clusters have been measured in the hydrogen-bonded NH and OH stretching regions to investigate the stable structures of 7AI(CH3OH)n (n=1–3) in the S0 state and the cooperativity of the H-bonding interactions in the H-bonded networks. The comparison of the IR-UV ion-dip spectra with IR spectra obtained by quantum chemistry calculations shows that 7AI(CH3OH)n (n=1–3) have cyclic H-bonded structures, where the NH group and the heteroaromatic N atom of 7AI act as the proton donor and proton acceptor, respectively. The H-bonded OH stretch fundamental of 7AI(CH3OH)2 is remarkably redshifted from the corresponding fundamental of (CH3OH)2 by 286 cm-1, which is an experimental manifestation of the cooperativity in H-bonding interaction. Similarly, two localized OH fundamentals of 7AI(CH3OH)3 also exhibit large redshifts. The cooperativity of 7AI(CH3OH)n (n=2,3) is successfully explained by the donor-acceptor electron delocalization interactions between the lone-pair orbital in the proton acceptor and the antibonding orbital in the proton donor in natural bond orbital (NBO) analyses. [ABSTRACT FROM AUTHOR]

Local low energy-loss functions (ELFs) of chemical ordered nanodomains in relaxor Pb(Mg1/3Nb2/3)O3 (PMN) were obtained by using Kramers–Krönig analysis of experimental electron low energy-loss spectra. Electronic structures and dielectric functions were calculated via ab initio calculation using the full-potential linearized augmented plane-wave method on a 30 atom PMN supercell with B-site cation ordering along the [111] direction. The theoretical ELFs are fundamentally in agreement with the experimental ELFs. Furthermore, we systematically elucidate all the peaks in the low ELF based on the ab initio calculated densities of states. It is found that the Nb 4d–O 2p hybridization is enhanced through ferroelectric transition, which makes the O 2p collective excitation energy upper shift in ELF, while Mg, also as the B-site ion, presents no covalent bonding effect with O. [ABSTRACT FROM AUTHOR]

An exactly solvable lattice model describing a binary solution is considered where rodlike molecules of types AA and BB cover the links of a honeycomb lattice, the neighboring molecular ends having three-body and orientation-dependent bonding interactions. At phase coexistence of AA-rich and BB-rich phases, the average fraction of each type of triangle of neighboring molecular ends is calculated exactly. The fractions of the different types of triangles are then used to deduce the local microscopic structure of the coexisting phases for a case of the model that contains two closed loops in the phase diagram. [ABSTRACT FROM AUTHOR]

Density functional theory combined with nonequilibrium Green’s function techniques was used to model the conduction through disubstituted benzenedithiol molecules bonded to leads composed of 3×3, 5×5 gold and 3×3 aluminum. For the disubstituted 3×3 Au-benzenedithiol-Au systems, the small lead cross section results in a region of nearly zero transmission from -0.4 to -0.2 eV, relative to EF, due to the absence of lead states. This feature results in negative differential resistance in the current-voltage curves and also causes the main peaks in the transmission spectra, which are dominated by the highest occupied molecular orbitals, to be centered near EF. The zero-bias transmissions for the disubstituted benzenedithiol, as well as currents at applied biases, correlate very well with the Hammett parameter σp, a quantity that relates the electron donating or withdrawing strength of a substituent. Calculations on disubstituted benzenedithiol connected to 5×5 Au leads produced transmission spectra that showed no gaps over the energy range considered and no negative differential resistance. The transmission in these cases also predominately involves the highest occupied molecular orbitals, and electron donating and withdrawing groups are able to increase and decrease current, respectively. However, there is no strong correlation between current and σp for this system. This suggests that the correlation observed in the 3×3 Au systems arises from the abrupt cutoff of the main transmission peaks near EF. The disubstituted 3×3 Al-benzenedithiol-Al systems displayed markedly different behavior from the Au analogs. Electron donating groups and H benzenedithiol-substituted systems display almost no transmission over the energy range considered. However, electron withdrawing group disubstituted benzenedithiol systems had significant peaks in the transmission spectra near EF, which are associated with the lowest-energy, unoccupied π-type molecular orbitals. Higher currents are calculated for cases where the substituents have π-type orbitals that are conjugated with the ring moiety of benzenedithiol. In all cases, the current through the 3×3 Al-benzenedithiol-Al systems is about a factor of 2 less than that through the analogous Au systems. These simulations reveal that the electrical conductance behavior through nanosystems of the type investigated in this work depends on the nature of the molecule as well as the size and composition of the leads to which it is connected. The results suggest that rational design of nanoelectronic systems might be possible under certain conditions but that structure-function relationships cannot be transferred from one system to another. [ABSTRACT FROM AUTHOR]