Characteristic Line Shape Research Articles

Controlling the Fano interference in a plasmonic lattice

We analyze the influence of near-field coupling on the formation of collective plasmon modes in a multilayer metallic nanowire array. It is shown that the spectral interference between super- and subradiant normal modes results in characteristic line shape modifications which are directly controlled by the spacing as well as the alignment of the stacked lattice planes. Moreover, a distinct near-field-induced reversal of particle plasmon hybridization is reported. Our numerical findings are in excellent agreement with experimental results.

Electromagnetomechanical coupling characteristics of plastoferrites

The impetus of this work was to investigate the electromagnetic and tensile properties of several commercially available plastoferrites (PFs) at ambient conditions. The approach involved selection of a set of PFs and measuring their complex effective permittivity ε=ε′−jε″ and permeability μ=μ′−jμ″ under uniaxial stress at microwave frequencies (0.1–4.5GHz) and room temperature. We analyze the ε and μ spectra for tensilely strained PFs up to 3%. Comparing our experimental ε data against several dielectric relaxational behaviors, we find that the main physics cannot be understood with a single relaxation mechanism. We then go on to consider the magnetic permeability spectra in the microwave range of frequencies and show that an appropriate magnetization mechanism is given by the gyromagnetic spin resonance mechanism. We use a combination of Bruggeman mean field analysis and Landau-Lifshitz-Gilbert modeling to reproduce the experimental bimodal line-shape characteristics of the effective complex magnetic permeability. These findings are discussed in light of the polydispersity in size of the ferrite gains contained in the PFs. The vibrating sample magnetometry investigations of the static magnetization are found to be consistent with this modeling. In addition, the analysis shows also how magnetized PFs respond to electromagnetic waves, and we evaluate the hysteretic behaviors of ε and μ. More importantly we show that the ε and μ measurements under stress can be explained in terms of a Gaussian molecular network model in the limit of low stress. The present results have important applications in magnetoactive smart composite materials, e.g., flexible circuit technology in the electronics industry (sensors, actuators, and micromechanical systems), functionalized artificial skin, and muscles for robotic applications.

Tetranuclear supramolecular structures containing phthalocyanine cores

A metal-free phthalocyanine with four pyridyl donor groups, bound through ethylthio ester bridges on the periphery, have been prepared. The pyridine donors were quaternized with iodomethane to a water-soluble tetracationic phthalocyanine. The tetranuclear supramolecular phthalocyanine was prepared by the coordination of peripheral pyridine donors with VO(acac)2. The paramagnetic tetranuclear structure was studied in powder and solution forms by the electron paramagnetic resonance (EPR) technique. Electron paramagnetic resonance studies, together with the other spectral data confirmed the presence of identical pyridine-coordinated VO(acac)2paramagnetic centers attached to the peripheral positions of the phthalocyanine core. The X-band EPR signals recorded from powder and solution forms of supramolecules have a characteristic line shape that proves the presence of axial symmetry around the paramagnetic vanadium ions. The anisotropic Lande splitting factors were calculated as g∥< g⊥< ge= 2.0023. Orbital energy levels for magnetic electrons were determined from theoretically fitted Spin Hamiltonian parameters.

Magnetic-Field Effects on the Size of Vortices below the Surface ofNbSe2Detected Using Low Energyβ-NMR

A low energy radioactive beam of polarized 8Li has been used to observe the vortex lattice near the surface of superconducting NbSe2. The inhomogeneous magnetic-field distribution associated with the vortex lattice was measured using depth-resolved beta-detected NMR. Below Tc, one observes the characteristic line shape for a triangular vortex lattice which depends on the magnetic penetration depth and vortex core radius. The size of the vortex core varies strongly with the magnetic field. In particular, in a low field of 10.8 mT, the core radius is much larger than the coherence length. The possible origin of these giant vortices is discussed.

Copper(II) and palladium(II) complexes of 2-amino-5-chlorobenzophenone and 2-(2-hydroxybenzylidene)amino-5-chlorobenzophenone-S-methyl-thiosemicarbazones

The S-methyl thiosemicarbazone derivatives of 2-amino-5-chlorobenzophenone and 2-(2-hydroxybenzylidene)amino-5-chlorobenzophenone (LI and LII) and their copper(II) and palladium(II) chelates were synthesized. The solid compounds, [Cu(LI)Cl]Cl · 2H2O, [Cu(LII)Cl]Cl · H2O, [Pd(LI)Cl]Cl, and [Pd(LII)Cl2], were characterized by elemental analysis, thermogravimetric measurements, electronic, i.r., 1H-n.m.r. and e.p.r. spectroscopy. The ligand behavior of the LI and LII explained by means of spectroscopic data. The experimental X-band e.p.r. spectra recorded from two different copper(II) ion coordinated powder complexes have characteristic line shapes that exhibit the axial symmetry around the paramagnetic ions. The theoretically well fitted spectra prove this case too. The absence of hyperfine signals has been attributed to the strong covalency effects of copper electrons with neighbouring N atoms. Orbital energy levels for magnetic electrons were determined from Spin Hamiltonian parameters. The anisotropic Lande splitting factors were specified in an order of \( {g_{| |}>g_{\bot}>2}\) and this case indicates that the unpaired electrons are located mainly in the \( {d_{x^{2}-y^{2}}}\) orbital.

Theory of Tunneling Spectroscopy in the Larkin-Ovchinnikov State

We present a theory of tunneling spectroscopy for normal metal/Larkin-Ovchinnikov state junctions in which the spatial periodic modulation in the pair potential amplitude is taken into account. The tunneling spectra show the characteristic line shapes reflecting the minigap structures under the periodic pair potentials depending on the boundary condition of the pair potentials at the junction interface. These features are qualitatively different from the tunneling spectra of the Fulde-Ferrell state. We propose an experimental setup which identifies the superconducting state of CeCoIn5.

Optical Properties and van der Waals - London Dispersion Interactions of Polystyrene Determined by Vacuum Ultraviolet Spectroscopy and Spectroscopic Ellipsometry

The interband optical properties of polystyrene in the vacuum ultraviolet (VUV) region have been investigated using combined spectroscopic ellipsometry and VUV spectroscopy. Over the range 1.5–32 eV, the optical properties exhibit electronic transitions we assign to three groupings, E1, E2, and E3, corresponding to a hierarchy of interband transitions of aromatic (π → π*), non-bonding (n → π*, n → σ*), and saturated (σ → σ*) orbitals. In polystyrene there are strong features in the interband transitions arising from the side-chain π bonding of the aromatic ring consisting of a shoulder at 5.8 eV (E1′) and a peak at 6.3 eV (E1), and from the σ bonding of the C–C backbone at 12 eV (E3′) and 17.1 eV (E3). These E3 transitions have characteristic critical point line shapes associated with one-dimensionally delocalized electron states in the polymer backbone. A small shoulder at 9.9 eV (E2) is associated with excitations possibly from residual monomer or impurities. Knowledge of the valence electronic excitations of a material provides the necessary optical properties to calculate the van der Waals–London dispersion interactions using Lifshitz quantum electrodynamics theory and full spectral optical properties. Hamaker constants and the van der Waals–London dispersion component of the surface free energy for polystyrene were determined. These Lifshitz results were compared to the total surface free energy of polystyrene, polarity, and dispersive component of the surface free energy as determined from contact angle measurements with two liquids, and with literature values. The Lifshitz approach, using full spectral Hamaker constants, is a more direct determination of the van der Waals–London dispersion component of the surface free energy of polystyrene than other methods.

Dynamical changeover of core exciton state of graphite and resonant x-ray emission spectrum: From shallow to deep level with symmetry breaking

A theoretical framework for the analysis of the resonant x-ray emission spectrum (RXES) of the core exciton state in graphite is presented. The strong electron-lattice coupling within the localized orbitals in the core exciton state together with the itinerant character of the electron in the conduction band is simultaneously taken into account in the extended vibronic cluster model. A full quantum mechanical calculation of the RXES and the x-ray absorption spectrum is carried out using the Green's function technique. The obtained spectral features well reproduce the experimental ones, including polarization dependence of RXES, its excitation energy dependence, and the characteristic absorption line shape.

Direct Solid-State NMR Spectroscopic Evidence for the NH4AlF4 Crystalline Phase Derived from Zeolite HY Dealuminated with Ammonium Hexafluorosilicate

Multinuclear (1)H, (19)F, and (27)Al MAS (magic angle spinning) and corresponding 2D HETCOR (heteronuclear correlation) NMR spectroscopy, in combination with powder XRD measurements, provide the direct evidence for the NH(4)AlF(4) crystalline phase, which was formed from zeolite HY dealuminated with an aqueous (NH(4))(2)SiF(6) solution at 80 degrees C. The NH(4)AlF(4) crystalline phase exhibits a characteristic second-order quadrupolar-induced (27)Al NMR line shape spreading from 0 to -90 ppm (in a magnetic field of 11.7 T) and two (19)F resonances at -151 and -166 ppm in the (19)F NMR spectrum. An( 27)Al quadrupolar coupling constant (C(Q)) of 9.5 MHz and an asymmetry parameter (eta) of 0.1 were identified, for the first time, for the NH(4)AlF(4) crystalline phase observed. On the basis of the (19)F{(27)Al} TRAPDOR (transfer population in double resonance) NMR results, the (19)F resonances at -151 and -166 ppm are therefore assigned to (19)F spins associated with the fluorines in the terminal Al-F and the bridging Al-F-Al groups, respectively.

Subcellular In Vivo 1H MR Spectroscopy of Xenopus laevis Oocytes

In vivo magnetic resonance (MR) spectra are typically obtained from voxels whose spatial dimensions far exceed those of the cells they contain. This study was designed to evaluate the potential of localized MR spectroscopy to investigate subcellular phenomena. Using a high magnetic field and a home-built microscopy probe with large gradient field strengths, we achieved voxel sizes of (180 μm) 3. In the large oocytes of the frog Xenopus laevis, this was small enough to allow the recording of the first compartment-selective in vivo MR spectra from the animal and vegetal cytoplasm as well as the nucleus. The two cytoplasmic regions differed in their lipid contents and NMR lineshape characteristics—differences that are not detectable with whole-cell NMR techniques. In the nucleus, the signal appeared to be dominated by water, whereas other contributions were negligible. We also used localized spectroscopy to monitor the uptake of diminazene acturate, an antitrypanosomal agent, into compartments of a single living oocyte. The resulting spectra from the nucleus and cytoplasm revealed different uptake kinetics for the two components of the drug and demonstrate that MR technology is on the verge of becoming a tool for cell biology.

Nonparabolicity and excitons in optical absorption of InN

We discuss the characteristic lineshape of the optical absorption of the novel “narrow-gap” InN in terms of the single-particle band structure and two-particle Coulomb interactions. More precisely, we explain the plateau in the imaginary part of the dielectric function, that follows the steep absorption onset, by the strong nonparabolicity of the conduction and light-hole bands near the zone center. The frequency range above 4.5 eV is dominated by higher optical interband transitions. The Coulomb attraction of optically excited electrons and holes leads to large redshifts of the spectral features and a strong coupling of the interband transitions.

Theoretical Investigation of the Temperature Dependence of the Fifth-Order Raman Response Function of Fluid and Liquid Xenon

The temperature dependence of the fifth-order Raman response function, R(5)(t1,t2), is calculated for fluid xenon by employing a recently developed time-correlation function (TCF) theory. The TCF theory expresses the two-dimensional (2D) Raman quantum response function in terms of a two-time, computationally tractable, classical TCF. The theory was shown to be in excellent agreement with existing exact classical MD calculations for liquid xenon as well as reproducing line shape characteristics predicted by earlier theoretical work. It is applied here to investigate the temperature dependence of the fifth-order Raman response function in fluid xenon. In general, the characteristic line shapes are preserved over the temperature range investigated (for the reduced temperature points T* = 0.5, 1.0, and 2.0); differences in the signal decay times and a large decline in intensity with decreasing temperature (and associated anharmonicity) are observed. In addition, there are some signature features that were not observed in earlier results for T* = 1. The most dramatic difference in line shape is observed for the polarization condition, xxzzxx, that shows a vibrational echo peak. In contrast, the fully polarized signal changes mainly in magnitude.

Resonant coupling of bound excitons with LO phonons in ZnO: Excitonic polaron states and Fano interference

We report on a photoluminescence observation of robust excitonic polarons due to resonant coupling of exciton and longitudinal optical (LO) phonon as well as Fano-type interference in high quality ZnO crystal. At low enough temperatures, resonant coupling of excitons and LO phonons leads to not only traditional Stokes lines (SLs) but also up to second-order anti-Stokes lines (ASLs) besides the zero-phonon line (ZPL). The SLs and ASLs are found to be not mirror symmetric with respect to the ZPL, strongly suggesting that they are from different coupling states of exciton and phonons. Besides these spectral features showing the quasiparticle properties of exciton-phonon coupling system, the first-order SL is found to exhibit characteristic Fano lineshape, caused by quantum interference between the LO components of excitonic polarons and the continuous phonon bath. These findings lead to a new insight into fundamental effects of exciton-phonon interactions.

Two-dimensional hyperfine sublevel correlation spectroscopy: Powder features for S = 1/2, I = 1

The lineshapes of two-dimensional magnetic resonance spectra of disordered or partially ordered solids are dominated by ridges of singularities in the frequency plane. The positions of these ridges are described by a branch of mathematics known as catastrophe theory concerning the mapping of one 2D surface onto another. We systematically consider the characteristics of HYSCORE spectra for paramagnetic centers having electron spin S = 1/2 and nuclear spin I = 1 in terms of singularities using an exact solution of the nuclear spin Hamiltonian. The lineshape characteristics are considered for several general cases: zero nuclear quadrupole coupling; isotropic hyperfine but arbitrary nuclear quadrupole couplings; coincident principal axes for the nuclear hyperfine and quadrupole tensors; and the general case of arbitrary nuclear quadrupole and hyperfine tensors. The patterns of singularities in the HYSCORE spectra are described for each case.

Applications of a time correlation function theory for the fifth-order Raman response function I: Atomic liquids

Multidimensional spectroscopy has the ability to provide great insight into the complex dynamics and time-resolved structure of liquids. Theoretically describing these experiments requires calculating the nonlinear-response function, which is a combination of quantum-mechanical time correlation functions R5(t1,t2) was expressed with a two-time, computationally tractable, classical TCF. Writing the response function in terms of classical TCFs brings the full power of atomistically detailed molecular dynamics to the problem. In this paper, the new TCF theory is employed to calculate the fifth-order Raman response function for liquid xenon and investigate several of the polarization conditions for which experiments can be performed on an isotropic system. The theory is shown to reproduce line-shape characteristics predicted by earlier theoretical work.

Fano interference with the alternating asymmetry parameter in time-domain experiments

It has been found that the time-domain reflection signal arising after the excitation of a bismuth single crystal at helium temperature by an ultrashort laser pulse exhibits Fano interference in the presence of the interaction between the lattice and charge degrees of freedom. This property is manifested in the characteristic spectral lineshape of the Fourier-transformed signal, whose asymmetry parameter is a periodic function of the delay time τ between the pumping and probing pulses. The most interesting property is the change of the sign of the asymmetry parameter when τ varies, which indicates that time reversal symmetry is broken. Various possible causes of the effect, observed for the first time, are discussed.

Electronic Raman scattering in unconventional density waves

We investigate the electronic Raman scattering in pure, quasi-one-dimensional conductors with a density wave ground state. In particular, we develop the theory of light scattering on spin and charge density waves, both conventional and unconventional. We calculate the electronic Raman response of the interacting-electron system with a single, highly anisotropic conduction band. The calculation is carried out in the mean-field approximation. In addition to the quasiparticle contribution, the electron-electron interaction is also included on the level of the random phase approximation. The contribution of collective modes and the effect of Coulomb screening are investigated. In analogy with unconventional superconductivity, the obtained Raman spectra---which are finite in the low-temperature phase possessing a gap, and vanish identically in the normal state---show unique and strong dependence on the polarization of the incoming and scattered light. We have found distinct, characteristic line shapes, especially in the unconventional situation, depending on the various scattering geometries and the particular momentum dependence of the density wave order parameter.

Collision-induced absorption by D2 pairs in the first overtone band at 77, 201 and 298 K

Collision induced absorption (CIA) spectra of pure D2 in the first overtone region from 5250 to 7250 \(\mbox{cm}^{-1}\), recorded at 77, 201 and 298 K, have been analyzed. The observed spectra at 77, 201 and 298 K were modelled by a total of 92, 214 and 267 components respectively of double vibrational transitions at room temperature of the type X2(J)+X0(J) and X1(J)+X1(J), where X is O, Q or S transitions. Profile analyses of the spectra were carried out using the Birnbaum-Cohen line-shape function for the individual components of the band, and characteristic line shape parameters were determined from the analysis. The observed and calculated profiles agree well over the whole overtone band, and the agreement is better than 97% in the three cases studied. Binary and ternary absorption coefficients were determined from the integrated absorption of the band.

Collision-induced first overtone band of D 2 in binary mixtures D 2–X where X is Ar, Kr, and Xe

Enhancement spectra of the collision-induced absorption in the first overtone region 5500–6750 cm −1 of D 2 in the D 2–Ar, D 2–Kr, and D 2–Xe binary mixtures were studied at 298 K for base densities of D 2 in the range 55–251 amagat and for partial densities of Ar, Kr, and Xe in the range 46–384 amagat. The observed spectra consist of the following quadrupolar transitions: O 2(3), O 2(2), Q 2 ( J), J = 1–5 and S 2 ( J), J = 0–5 of D 2. Binary and ternary absorption coefficients were determined from the integrated absorption coefficients of the band. Profile analyses of the spectra were carried out using the Birnbaum–Cohen (BC) lineshape function and characteristic lineshape parameters were determined from the analyses.

Collision-induced first overtone band of [formula omitted] in binary mixtures [formula omitted]– [formula omitted] and [formula omitted]–CO

Enhancement spectra of the collision-induced absorption (CIA) of H 2 in its first overtone region 7500– 9500 cm - 1 in binary mixtures H 2 – N 2 and H 2 –CO were studied at 298 K for base densities of H 2 in the range 89–145 amagat and for partial densities of N 2 and CO in the range 19–392 amagat. The observed spectra confirm that the isotropic overlap induction is absent in the 2–0 band of H 2 unlike in the CIA spectra of the fundamental band of H 2 . Binary and ternary absorption coefficients were determined from the integrated absorption coefficients of the band. Enhancement absorption profiles of H 2 – N 2 and H 2 –CO consist of a total of 434 components of quadrupolar double transitions. Profile analysis of the spectra was carried out using Birnbaum–Cohen line shape function for the individual components of the band and characteristic line shape parameters were determined from the analysis.