Line Shape Of Spectra Research Articles

ESR spectroscopy as a new method to analyze the synergy between two different nanofillers dispersed in an elastomer matrix

In this study electron spin resonance (ESR) investigations on hybrid natural rubber based nanocomposites loaded with 2 phr of multi-walled carbon nanotubes (MWCNT) and various concentrations of expanded organically modified montmorillonite (EOMt) (0; 8 and 16 phr) were reported. The temperature dependence of the resonance line parameters in the range 160–353 K was analyzed. From the obtained results it was evident that the presence of the EOMt influences the appearance of the ESR spectra. This influence makes it possible to assess the state of dispersion of the hybrid nanofiller in the rubber matrix only by analyzing the line shape of the resonance ESR spectra. The Lorenzian line shape indicates good dispersion of the nanofillers while Dysonin line shape suggests re-agglomeration. The increase of the g-factor, or resonance line position values, when EOMt is present in the matrix suggests that the EOMt and MWCNT interact in such a way that the content of the defects in the multi-walled carbon nanotubes decreases.

Hidden-strange molecular states and the Nϕ bound states via a QCD van der Waals force

In this work, we study the hidden-strange molecular states composed of a baryon and a vector meson in a coupled-channel $N\rho-N\omega-N\phi-\Lambda K^*-\Sigma K^*$ interaction. With the help of the effective Lagrangians which coupling constants are determined by the SU(3) symmetry, the interaction is constructed and inserted into the quasipotential Bethe-Salpeter equation to search for poles in the complex plane, which correspond to molecular states. Two poles are found with a spin parity $3/2^-$ near the $N\rho$ and the $\Sigma K^*$ thresholds, which can be related to the $N(1700)$ and the $N(2100)$, respectively. No pole near the $N\phi$ threshold can be found if direct interaction between a nucleon and $\phi$ meson is neglected according to the OZI rule. After introducing the QCD van der Waals force between a nucleon and $\phi$ meson, a narrow state can be produced near the $N\phi$ threshold. Inclusion of the QCD van der Waals force changes the line shape of the invariant mass spectrum in the $N\phi$ channel leading to a worse agreement with the present low-precision data. Future experiments at BelleII, JLab, and other facilities will be very helpful to clarify the existence of these possible hidden-strange molecular states.

EPR Imaging of Metallic Lithium and its Application to Dendrite Localisation in Battery Separators

Conduction Electron Paramagnetic Resonance Imaging (CEPRI) is presented as a sensitive technique for mapping metallic lithium species. The method is demonstrated using different samples that are either thick or thin compared to the microwave skin depth. As a thin sample, microstructured metallic lithium deposits in a lithium-ion battery (LIB) separator were analysed, illustrating the capabilities of CEPRI by obtaining a high-resolution image with an image resolution in the micrometre range. Limitations and intricacies of the method due to non-linear effects caused by the skin effect are discussed based on images of surface patterns on thick metallic lithium samples. The lineshape of the EPR spectrum is introduced as a proxy to determine the suitability of CEPRI for the quantitative visualisation of metallic lithium deposits. The results suggest that CEPRI is particularly suited to analyse the spatial distribution of microstructured Li that forms during charging and discharging of LIB cells, including the localization of the point of failure in the case of an internal cell short circuit caused by dendrites.

EPR study of RE3+ (RE = Nd, Gd, Dy) doped CdMoO4 single crystal

Abstract The electron paramagnetic resonance (EPR) studies of RE3+ (RE = Nd, Gd, Dy) doped CdMoO4 single crystals grown by Czochralski method were carried out in 4–300 K temperature range. Analysis of EPR spectra lineshapes and resonance field dependence on crystal orientation in an external magnetic field allowed allocate the RE3+ ions to the low symmetry site of Cd2+ in CdMoO4 crystal. Additionally, RE3+ complex magnetic entities created due to charge compensation, were registered. In the case of Nd3+ doped CdMoO4 crystal the values of g spectroscopic matrix were calculated and the influence of the excited states via the Orbach process was observed.

Coupled-mode theory of field transfer processes in surface plasmon resonance structures

We study the response of the metal-dielectric planar structures supporting surface plasmon polariton modes to an external electromagnetic field. Analysing the field transfer processes within the coupled-mode theory, we demonstrate the role of non-resonant and resonant responses in the appearance of Fano line shapes in spectra of the metal-dielectric interfaces, Otto and Kretschmann ATR configurations.

M1 and E2 transition rates from core-excited states in semi-magic 94Ru

Lifetimes of high-spin states have been measured in the semi-magic $(N=50)$ nucleus 94Ru. Excited states in 94Ru were populated in the 58Ni(40Ca, 4p)94Ru* fusion-evaporation reaction at the Grand Accelerateur National d’Ions Lourds (GANIL) accelerator complex. DSAM lifetime analysis was performed on the Doppler broadened line shapes in energy spectra obtained from $\gamma$ -rays emitted while the residual nuclei were slowing down in a thick 6mg/cm^2 metallic 58Ni target. In total eight excited-state lifetimes in the angular momentum range $I = (13-20)\hbar$ have been measured, five of which were determined for the first time. The corresponding B(M1) and B(E2) reduced transition strengths are discussed within the framework of large-scale shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.

Emission spectra of hexagonal zinc oxide microrods due to resonant modes

Experimental observation and theoretical analysis of the whispering gallery mode (WGM) related emission spectra of ZnO microrods with a hexagonal cross-section are reported. ZnO microrods of various sizes are fabricated, and their individual geometric information (including the inner radius, edge profile modification, and tilt angle) are characterized via scanning electron microscopy (SEM). The photoluminescence spectra in the visible range (with energies between 1.77 and 2.76 eV) are compared with theoretical simulation based on Green function calculation within a nearly complete set of basis functions. WGM resonance peaks for TE and TM modes of five different sizes of microrods are analyzed. By using the SEM determined geometry with a slight adjustment, we obtain realistic simulation of the line shapes of the emission spectra, which agree well with experimental observation. To gain better understanding of the WGM resonance modes, we also calculate the WGM resonance profile of ZnO microrods with the cylindrical cross-section for both TE and TM modes for comparison.

Benzene‐d6 and toluene‐d8 as guest molecules in micropores of a layered zirconium phosphonate: 2H, 13C{1H}, and 31P{1H} solid‐state NMR, deuterium NMR relaxation, and molecular motions

For the first time, pore spaces in the Zr (IV) phosphonate (1) as a representative of layered metal (IV) phosphonate materials have been investigated by studying mobility of guest molecules, benzene-d6 , and toluene-d8 . Guest molecules located in micropores of 1 have been characterized by solid-state 13 C{1 H} and 2 H NMR spectra in static samples with varying temperatures. At moderately low temperatures, the benzene and toluene molecules experience fast isotropic reorientations and show the motionally averaged liquid-like carbon and deuterium line shapes in the NMR spectra. At lower temperatures, two anisotropic motional modes have been found for benzene molecules by analyzing the 2 H NMR line shapes: the well-known in-plane C6 rotation and composite motions. Interpretation of the variable-temperature 2 H T1 relaxation times identifies the composite motions as 120° flips around the C6 axis perpendicular to the molecular plane and the rotations around the molecular para-C-C axis. The data obtained resulted in the idealized (cylinder-shaped) model of micropores in compound 1 with the diameter of 20-30Å. Furthermore, the activation energy of 20.1kJ/mol determined for the benzene motions classifies the molecule-surface interactions as weak but enough for absorption.

Linear absorption spectra of solvated thiouracils resolved at the hybrid RASPT2/MM level

On the example of 2-, 4- and 2,4-thiouracil we demonstrate the performance of the RASPT2/RASSCF protocol in reproducing the spectral positions and line shapes of linear absorption spectra that have been recorded in water and documented in this work. Through a QM/MM scheme coupled to a room-temperature Wigner sampling we simulate condensed phase spectra, permitting to compare our results against experiments. We discuss the sensitivity of the simulations to: a) the active space size by pushing the limits beyond the full-valence active spaces; b) the consideration of “dark” nπ∗-states in the state averaging; c) the flavor of RASPT2 technique; d) the basis set. The benchmarking demonstrates that full-π valence active spaces tend to red-shift the absorption band. Increasing the active space rectifies the problem and we obtain near-quantitative agreement between our experiments and calculations. We, furthermore, demonstrate that the choice of RASPT2 flavor has to be made through rigorous benchmarking.

On the Mechanism of Magnesium Storage in Micro- and Nano-Particulate Tin Battery Electrodes.

This study reports on the electrochemical alloying-dealloying properties of Mg2Sn intermetallic compounds. 119Sn Mössbauer spectra of β-Sn powder, thermally alloyed cubic-Mg2Sn, and an intermediate MgSn nominal composition are used as references. The discharge of a Mg/micro-Sn half-cell led to significant changes in the spectra line shape, which is explained by a multiphase mechanism involving the coexistence of c-Mg2Sn, distorted Mg2−δSn, and Mg-doped β-Sn. Capacities and capacity retention were improved by using nanoparticulate tin electrodes. This material reduces significantly the diffusion lengths for magnesium and contains surface SnO and SnO2, which are partially electroactive. The half-cell potentials were suitable to be combined versus the MgMn2O4 cathodes. Energy density and cycling properties of the resulting full Mg-ion cells are also scrutinized.

Frequency-Comb Based Double-Quantum Two-Dimensional Spectrum Identifies Collective Hyperfine Resonances in Atomic Vapor Induced by Dipole-Dipole Interactions.

Frequency-comb based multidimensional coherent spectroscopy is a novel optical method that enables high-resolution measurement in a short acquisition time. The method's resolution makes multidimensional coherent spectroscopy relevant for atomic systems that have narrow resonances. We use double-quantum multidimensional coherent spectroscopy to reveal collective hyperfine resonances in rubidium vapor at 100 °C induced by dipole-dipole interactions. We observe tilted and elongated line shapes in the double-quantum 2D spectra, which have never been reported for Doppler-broadened systems. The elongated line shapes suggest that the signal is predominately from the interacting atoms that have a near zero relative velocity.

EPR Evidence of Liquid Water in Ice: An Intrinsic Property of Water or a Self-Confinement Effect?

Liquid water (LW) existence in pure ice below 273 K has been a controversial aspect primarily because of the lack of experimental evidence. Recently, electron paramagnetic resonance (EPR) has been used to study deeply supercooled water in a rapidly frozen polycrystalline ice. The same technique can also be used to probe the presence of LW in polycrystalline ice that has formed through a more conventional, slow cooling one. In this context, the present study aims to emphasize that in case of an external probe involving techniques such as EPR, the results are influenced by the binary phase (BP) diagram of the probe-water system, which also predicts the existence of LW domains in ice, up to the eutectic point. Here we report the results of our such EPR spin-probe studies on water, which demonstrate that smaller the concentration of the probe stronger is the EPR evidence of liquid domains in polycrystalline ice. We used computer simulations based on stochastic Liouville theory to analyze the lineshapes of the EPR spectra. We show that the presence of the spin probe modifies the BP diagram of water, at very low concentrations of the spin probe. The spin probe thus acts, not like a passive reporter of the behavior of the solvent and its environment, but as an active impurity to influence the solvent. We show that there exists a lower critical concentration, below which BP diagram needs to be modified, by incorporating the effect of confinement of the spin probe. With this approach, we demonstrate that the observed EPR evidence of LW domains in ice can be accounted for by the modified BP diagram of the probe-water system. The present work highlights the importance of taking cognizance of the possibility of spin probes affecting the host systems, when interpreting the EPR (or any other probe based spectroscopic) results of phase transitions of host, as its ignorance may lead to serious misinterpretations.

J-Resonance Line Shape of Magnetic Field-Affected Reaction Yield Spectrum from Charge Recombination in a Linked Donor–Acceptor Dyad

Magnetic field effects (MFEs) allow detailed insight into spin conversion processes of radical pairs that are formed, for example, in all charge separation processes, and are supposed to play the key role in avian navigation. In this work, the MFE of charge recombination in the charge-separated state of a rigid donor–bridge–acceptor dyad was analyzed by a classical and a quantum theoretical model and represents a paradigm case of understanding spin chemistry with unprecedented detail. The MFE is represented by magnetic field-affected reaction yield (MARY) spectra that exhibit a sharp resonance, resulting from S/T level crossing as the Zeeman splitting equals twice the exchange interaction. Although in the classical kinetic model, the spin conversion processes between the four singlet and triplet substates are shown for the first time to obey an identical generalized energy dependence, quantum theory proves that the MARY resonance line is composed of relaxation, coherent hyperfine induced spin mixing, and S/T dephasing contributions.

Element-specific observation of the ferromagnetic ordering process in UCoAl via soft x-ray magnetic circular dichroism

We have performed soft x-ray magnetic circular dichroism (XMCD) experiments on the itinerant-electron metamagnet UCoAl at the U $4d\ensuremath{-}5f({N}_{4,5})$ and Co $2p\ensuremath{-}3d({L}_{2,3})$ absorption edges in order to investigate the magnetic properties of the U $5f$ and Co $3d$ electrons separately. From the line shape of the XMCD spectrum, it is deduced that the orbital magnetic moment of the Co $3d$ electrons is unusually large. Through the systematic temperature $(T)$- and magnetic field $(H)$-dependent XMCD measurements, we have obtained two types of the magnetization curve as a function of $H$ and $T$ (M-H curve and M-T curve, respectively). The metamagnetic transition from a paramagnetic state to a field-induced ferromagnetic state was clearly observed under 15 K at ${H}_{\mathrm{M}}$. The value of the ${H}_{\mathrm{M}}$ and its $T$ dependence agree well between the U and Co sites, and the bulk magnetization. Whereas, we have discovered the remarkable differences in the M-H and M-T curves between the U and Co sites. The present findings clearly show that the role of the Co $3d$ electrons should be considered more carefully in order to understand the origin of the magnetic ordering in UCoAl.

First-principles study of the optical properties of YPO4 crystal with oxygen vacancies

In this study, in order to obtain more accurate optical spectrum line shapes, the defect formation energies of oxygen vacancies in YPO4 crystals with three different charges (0, +1, +2) were calculated using the finite-size correction scheme. The optical properties of the F center and F+ center were studied based on electron–phonon coupling. The emission peak calculated for the F+ center was close to the experimental value. The luminescence and absorption peaks were in the ultraviolet region for the F and F+ centers. We predicted that the absorption peak at 140 nm was related to the F center and that at 152 nm to the F+ center.

O2-O2 and O2-N2 collision-induced absorption mechanisms unravelled.

Collision-induced absorption is the phenomenon in which interactions between colliding molecules lead to absorption of light, even for transitions that are forbidden for the isolated molecules. Collision-induced absorption contributes to the atmospheric heat balance and is important for the electronic excitations of O2 that are used for remote sensing. Here, we present a theoretical study of five vibronic transitions in O2-O2 and O2-N2, using analytical models and numerical quantum scattering calculations. We unambiguously identify the underlying absorption mechanism, which is shown to depend explicitly on the collision partner-contrary to textbook knowledge. This explains experimentally observed qualitative differences between O2-O2 and O2-N2 collisions in the overall intensity, line shape and vibrational dependence of the absorption spectrum. It is shown that these results can be used to discriminate between conflicting experimental data and even to identify unphysical results, thus impacting future experimental studies and atmospheric applications.

Cyanamide as an Infrared Reporter: Comparison of Vibrational Properties between Nitriles Bonded to N and C Atoms.

Infrared (IR) probes based on terminally blocked β-cyanamidoalanine (AlaNHCN) 1 and p-cyanamidophenylalanine (PheNHCN) 2 were synthesized, and the vibrational properties of their CN stretch modes were studied using Fourier transform infrared (FTIR) and femtosecond IR pump-probe spectroscopies in combination with quantum chemical calculations. From FTIR studies, it is found that the transition dipole strengths of the cyanamide (NHCN) group in 1 and 2 are much larger than those of the nitrile (CN) group but comparable to those of the isonitrile (NC) and azido (N3) groups in their previously studied analogs. The CN stretch frequencies in 1 and 2 are red-shifted from those in their nitrile analogs but more blue-shifted from the NC and N3 stretch frequencies in their isonitrile and azido analogs. The much larger transition dipole strength and the red-shifted frequency of the cyanamide relative to nitrile group originates from the n → π* interaction between the N atom's nonbonding (n) and CN group's antibonding (π*) orbitals of the NHCN group. Unlike aliphatic cyanamide 1, aromatic cyanamide 2 shows a complicated line shape of the CN stretch spectra. Such a complicated line shape arises from the Fermi resonance between the CN stretch mode of the NHCN group and one of the overtones of the phenyl ring vibrations and can be substantially simplified by deuteration of the NHCN into NDCN group. From IR pump-probe experiments, the vibrational lifetimes of the CN stretch mode in 1 were determined to be 0.58 ± 0.04 ps in D2O and 0.89 ± 0.09 ps in H2O and those in 2 were determined to be 1.64 ± 0.13 ps in CH3OD/dimethyl sulfoxide and 0.30 ± 0.05 and 2.62 ± 0.26 ps in CH3OH. The short time component (0.30 ± 0.05 ps) observed for 2 in CH3OH is attributed to the vibrational relaxation through Fermi resonance. These vibrational lifetimes are close to those of the nitrile and azido groups but shorter than those of the isonitrile group. Consequently, cyanamide behaves like an apparent vibrational hybrid of nitrile and isonitrile in that cyanamide is similar to nitrile in vibrational frequency and lifetime but to isonitrile in transition dipole strength. It is believed that cyanamide has the potential to be a strongly absorbing IR reporter of the conformational and environmental structure and dynamics of biomolecules in comparison to nitrile, a weak absorber.

Ultralow-power on-chip all-optical Fano diode based on uncoupled nonlinear photonic-crystal nanocavities

We achieved an ultralow-power Fano-like diode in integrated photonic circuits through two cascaded and uncoupled photonic-crystal microcavities, coated with a nonlinear layer constructed from polycrystalline indium-tin oxide doped with gold nanoparticles. The multicomponent nanocomposite layer helps to obtain an extremely large nonlinearity enhancement on account of the quantum confinement effect, hot-electron injection, and local-field enhancement effect. Thus, the strong nonlinearity enhancement, asymmetric Fano-like spectrum lineshape, and asymmetric light confinement for the forward and backward incidence cases guarantee the nonreciprocal transmission of signal light. A compact size of 7 μm is maintained for the photonic-crystal microcavities and the transmission contrast reached 15 dB. Besides, we achieved 1.5 kW cm−2 operating threshold intensity (cut down by a thousand times). This work assists chip-integrated optical computing on the basis of nonlinear photonic-crystal microcavities.

Evaluation of the Built-in Voltage of a Au/n-GaAs Schottky Barrier Diode by Using Electroreflectance Spectroscopy

The built-in voltage (V bi ) of a Au/n-GaAs Schottky barrier diode was examined by using electroreflectance (ER) spectroscopy. The ER spectra were measured at various modulation voltages (v ac ) and dc bias voltages (V bias ). The interface electric fields (E i ) were obtained from the observed Franz-Keldysh oscillations (FKO) in the ER spectra. When v ac was increased, the amplitudes of the ER spectra varied linearly, but the line shapes of the ER spectra did not change. E i decreased from 19.3 × 104 V/cm to 4.39 × 104 V/cm with increasing V bias from −0.5 V to 0.6 V. From the relationship between V bias and E i 2 , the V bi and the carrier concentration (n) were found to be 0.70 V and 2.4 × 1016 cm −3, respectively.

Flexibly tunable high-quality-factor induced transparency in plasmonic systems

The quality (Q) factor and tunability of electromagnetically induced transparency (EIT)-like effect in plasmonic systems are restrained by the intrinsic loss and weak adjustability of metals, limiting the performance of the devices including optical sensor and storage. Exploring new schemes to realize the high Q-factor and tunable EIT-like effect is particularly significant in plasmonic systems. Here, we present an ultrahigh Q-factor and flexibly tunable EIT-like response in a novel plasmonic system. The results illustrate that the induced transparency distinctly appears when surface plasmon polaritons excited on the metal satisfy the wavevector matching condition with the guided mode in the high-refractive index (HRI) layer. The Q factor of the EIT-like spectrum can exceed 2000, which is remarkable compared to that of other plasmonic systems such as plasmonic metamaterials and waveguides. The position and lineshape of EIT-like spectrum are strongly dependent on the geometrical parameters. An EIT pair is generated in the splitting absorption spectra, which can be easily controlled by adjusting the incident angle of light. Especially, we achieve the dynamical tunability of EIT-like spectrum by changing the Fermi level of graphene inserted in the system. Our results will open a new avenue toward the plasmonic sensing, spectral shaping and switching.