Line Shape Of Spectra Research Articles

Effect of Rotational Couplings on Vibrational Spectrum Line Shape of the Bending Mode in Low-Density Supercritical Water: Density and Hydrogen Isotopes Dependencies

The effect of rotations on the line shape of the bending vibrational spectrum for supercritical water was analyzed using classical molecular dynamics simulation for the flexible point-charge SPC/Fw model. The experimental infrared spectrum of the bending mode at the low densities of 0.01–0.04 g·cm−3 and at 400 °C was essentially reproduced without any other assumptions. The spectrum line shape at low densities consists of two broad rotational bands due to the rotational couplings, as in the case of the O–H stretch mode. This is due to the time-scale separation breakdown but is not due to the presence of any definite clusters. The rotational couplings become more significant at higher temperatures. The separations between the bending band center and the rotational broad side-bands are found to be linearly correlated with the inverse of the total moment of inertia of the water isotopic species, which is clear molecular-level evidence for the rotational couplings.

The lineshape of the electronic spectrum of the green fluorescent protein chromophore, part I: gas phase.

In this work we present the vibrationally resolved optical absorption spectrum of p-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI), the green fluorescent protein (GFP) chromophore, computed at several levels of theory, including time-dependent DFT with various functionals and basis sets, CASSCF, CASPT2 and XMCQDPT2. We also investigated what happens to the spectrum if the ground- and excited-state geometries are optimized at different levels of theory (mixed approach), as has been used previously. The vibrationally resolved absorption spectra obtained by DFT, CASPT2 and XMCQDPT2 are very similar and consist of a main absorption peak and a shoulder that is ∼1500 cm(-1) higher in energy. The vibrational progression increases moderately with temperature. These spectra are in qualitative agreement with experimental action spectra, but much narrower and lack the long tail in the blue, even at high temperatures. Because our calculated emission spectra, which are equally narrow, are in good agreement with the emission of green fluorescent protein at 253 K, we argue that the action spectrum are too broad to be considered as the absorption spectrum. The CASSCF method and the mixed approaches overestimate the vibrational progressions with respect to CAM-B3LYP, CASPT2 and XMCQDPT2, due to inaccuracies in the geometric S0 →S1 displacements. Finally, we computed the vibronic spectra of four chromophore analogues with different substitutions on the rings and found that these substitutions hardly affect the lineshape in vacuum.

Effect of apodization on FT-ICR mass spectrometry analysis of petroleum

Apodization is a generally applied signal processing method in FT-ICR MS (Fourier transform ion cyclotron resonance mass spectrometry) analysis for complex petroleum samples that is used to lower the spectral leakage and smoothen the spectrum line shape. Present study evaluates the effect of apodization on the FT-ICR MS results through a systematic examination on both simulated and actual heavy petroleum signals. The result shows that the resolving power, instead of the dynamic range, is the key factor for heavy petroleum FT-ICR MS analysis due to the severe peak overlapping. Window functions with high dynamic range will reduce the resolving power so that many of the species cannot be detected. The improvement on accuracy of apodization with peak intensity is negligible and all the window functions have similar intensity error. Low dynamic range window functions perform better for FT-ICR MS analysis since they have less resolving power reduction and the spectral leakage is eliminated to ensure correct peak selection. Sine-bell and low beta value Kaiser window functions are recommended for complex mixtures.

Fano-like line shape of spontaneous emission spectrum in a weakly driven two-level atom

It has been shown that the Fano-like profile of spontaneous emission spectrum can be obtained in a weakly driven two-level atom under certain conditions. Coherent control of the spectral ‘hole’ or dark line generated in the asymmetric line shape can also be achieved by varying those conditions.

Quantum interference in thermoelectric molecular junctions: A toy model perspective

Quantum interference (QI) phenomena between electronic states in molecular circuits offer a new opportunity to design new types of molecular devices such as molecular sensors, interferometers, and thermoelectric devices. Controlling the QI effect is a key challenge for such applications. For the development of single molecular devices employing QI effects, a systematic study of the relationship between electronic structure and the quantum interference is needed. In order to uncover the essential topological requirements for the appearance of QI effects and the relationship between the QI-affected line shape of the transmission spectra and the electronic structures, we consider a homogeneous toy model where all on-site energies are identical and model four types of molecular junctions due to their topological connectivities. We systematically analyze their transmission spectra, density of states, and thermoelectric properties. Even without the degree of freedom for on-site energies an asymmetric Fano peak could be realized in the homogeneous systems with the cyclic configuration. We also calculate the thermoelectric properties of the model systems with and without fluctuation of on-site energies. Even under the fluctuation of the on-site energies, the finite thermoelectrics are preserved for the Fano resonance, thus cyclic configuration is promising for thermoelectric applications. This result also suggests the possibility to detect the cyclic configuration in the homogeneous systems and the presence of the QI features from thermoelectric measurements.

Photoluminescence of Nanoporous GaN Films Prepared by Electrochemical Etching

Nanoporous (NP) GaN is prepared by electrochemical etching on a GaN epilayer grown on a sapphire substrate by metal-organic chemical vapor deposition. Scanning electron microscopy reveals that the average pore diameter and inter-pore spacing are approximately 25 and 45 nm, respectively. The photoluminescence (PL) spectra show that in contrast to the initial as-grown GaN epilayer, the NP GaN exhibits a high near-band-edge UV intensity, significant relaxation of compressive strain, and a lower yellow luminescence intensity. Both the line shape and line width of the PL spectra are almost the same for these two samples. The high quality of the NP GaN can be explained by the enhancement of the PL extraction efficiency and the decrease of impurity and defect density after etching.

Effect of the Particle Size on the Microwave Absorption in the Yttrium-Iron Garnet

A comparative study between micropowders and nanopowders of Y3Fe5O12 (YIG) by means of ferromagnetic resonance (FMR) is reported. Significant changes in lineshape of the FMR spectra between both samples are observed, in particular, the absorption mode in nanopowders have an internal structure which can be associated with magnetostatic modes. Additionally, a method to measure the non-resonant microwave absorption, as function of an applied magnetic field around zero field, known as the low-field microwave absorption (LFMA) is also employed. LFMA technique is used to give a further knowledge on the YIG samples, showing their main characteristics highlighted. These techniques are powerful tools for the research of magnetic materials at microwave frequencies.

Line-Shape Analyses of Solid-state 17O NMR Spectra for Hexagonal Ice

We present the results of experimental and theoretical investigations of line shapes in solid-state 17O NMR spectra of hexagonal ice, Ih. Stationary 17O NMR spectra of Ih at temperatures from 143 to 280 K were obtained at 11.7 and 16.4 T. Line shapes changed drastically as the temperature was increased from 143 to 243 K; at 253 K and above, pseudo-isotropic line shapes appear, indicating the presence of reorientational motions. We find that Ratcliffe’s model, which involves twelve orientations and four-step jumps for water reorientational motions, is effective for analyzing the NMR spectra at temperatures below 243 K. The present analysis demonstrates that the isotropic line shapes arise from proton disorder with respect to the solid-state 17O NMR time scale, producing pseudoicosahedral motional averaging that can completely average out second-order quadrupole interactions.

Complex Coacervation of Polyelectrolytes Studied by Spin‐Label EPR Spectroscopy

Spin‐labeled poly(ethylene‐alt‐maleic acid) (SL‐P(E‐alt‐MA)) with 2.5 mol% spin‐labeled repeat units is prepared to study the interaction of this polyanion with an oppositely charged polyelectrolyte by electron paramagnetic resonance (EPR) spectroscopy. The internal rotation of the spin label and the segmental rotational mobility of the polyanion in aqueous solution are determined by simulating the line shapes of the experimental EPR spectra as a function of temperature. The complex formation of SL‐P(E‐alt‐MA), a weak polyanion, with the strong polycation poly(diallyldimethylammonium chloride) (PDADMAC) is studied, in dependence of the mixing ratio. If the spin‐labeled polyanion is the excess component, the spectrum of a slow‐moving component is superimposed by the spectrum of a fast‐moving component. In the opposite case, the spectra are dominated by a slow‐moving component. image

Variations of nitric oxide in the mesosphere and lower thermosphere over Antarctica associated with a magnetic storm in April 2012

We report extreme enhancements of the nitric oxide (NO) column density observed with the ground-based millimeter-wave spectroscopic radiometer installed at Syowa Station, Antarctica, during a large geomagnetic storm in April 2012. From the NO spectrum line shape and NO column density relationship with solar radiation, we concluded that the NO was emitted in the altitude range between 75 km and 100 km. The column density of NO gradually increased during the recovery phase. In addition to variations on a time frame of several days, we found diurnal variations. The increase of NO was related to precipitated electrons in the energy range of 30–300 keV observed by Polar-orbiting Operational Environmental Satellite (POES)/The Meteorological Operational (METOP). We found a rapid response (within 1 h) and a one-to-one correspondence between them. For the first time, we show that a remarkable increase of the column density of NO is caused by dawn-dusk asymmetry of the plasma sheet electrons.

First-principle computation of absorption and fluorescence spectra in solution accounting for vibronic structure, temperature effects and solvent inhomogenous broadening

We compute the line shape of absorption and emission electronic spectra of two different dyes, Coumarin C153 and N-methyl-6-Quinolinium betaine accounting for the vibronic structure, temperature effects and polar solvent inhomogeneous broadening, without using any phenomenological parameter. We exploit a number of recent developments including a time-dependent (TD) approach to the computation of vibronic spectra that provides fully converged line shapes at finite temperature accounting for both Duschinsky and Herzberg–Teller effects, and the state-specific (SS) implementation of Polarizable Continuum Model (PCM). This latter is adopted to compute the solvent reorganization energy connected to inhomogenoeus broadening. We compute the absorption and fluorescence spectra in the gas-phase, non-polar and polar solvents analyzing the relative importance of different sources of broadening. To this end we investigate the performance of TD Density Functional Theory, Complete Active Space Self Consistent Field (CASSCF) and Complete Active Space second-order Perturbation Theory (CASPT2) methods in the computation of inhomogeneous broadening.

Computational Investigation on the Spectroscopic Properties of Thiophene Based Europium β-Diketonate Complexes.

The adiabatic transition energies from the lowest triplet states of four Europium tris β-diketonate/phenantroline complexes have been determined in vacuo and in dicholomethane solution by the ΔSCF approach at the density functional theory level, using the PBE1PBE and the CAM-B3LYP hybrid functionals. The calculated adiabatic transition energies have been compared with the experimental 0-0 transitions of each complex determined from phosphorescence spectra of the corresponding Gd(3+) complexes and followed by direct comparison between simulated and experimental spectra line shapes. For compound 1, the Eu(TTA)3Phen system, triplet states other than the lowest one and conformational isomers other than the one present in the crystallographic structure have been considered. In the crystallographic structure, this compound presents three quasi-degenerate low energy triplet states, differing for the TTA ligand where the two unpaired electrons are localized and showing close adiabatic transition energies. For compound 1, the lowest triplet states of the four investigated conformational isomers show similar characteristics and close adiabatic transition energies. On the basis of these results, an investigation of compounds 2-4 (Eu(Br-TTA)3Phen, Eu(DTDK)3Phen, and Eu(MeT-TTA)3) has been performed by considering only the isomer present in the crystallographic structure and only the lowest triplet state of each compound. For compounds 1-3, the energies of the lowest triplet states calculated by both functionals in solution including zero-point energy corrections well reproduce the experimental trends as well as the values of the adiabatic transition energies: CAM-B3LYP, the best performing functional, provides energies of the lowest triplet state with deviations from experiments lower than 1200 cm(-1). Also, the calculated vibrationally resolved phosphorescence spectra and UV-vis absorptions well reproduce the main features of their experimental counterparts. Significant differences between calculated and experimental results are observed for compound 4, for which difficulties in the experimental determination of the triplet state energy were encountered: our results show that the negligible photoluminescence quantum yield of this compound is due to the fact that the energy of the most stable triplet state is significantly lower than that of the resonance level of the Europium ion, and thus the energy transfer process is prevented. These results confirm the reliability of the adopted computational approach in calculating the energy of the lowest triplet state energy of these systems, a key parameter in the design of new ligands for lanthanide complexes presenting large photoluminescence quantum yields.

Fano Resonance of the Symmetry‐Reduced Metal Bar Grating Structure

We demonstrate that Fano resonance and even multipole Fano resonance can be obtained in a symmetry‐reduced structure composed of gold bars with different bar sizes or bar shapes on a layer of dielectric. There is a transparency window opened within the frequency region of the absorptive dipole resonance by metallic bars, as long as the narrow grating waveguide mode induced by reducing symmetry is coincided in spectrum with the dipole resonance such that a destructive interference happens between these two resonant modes. Line shape of the transmission spectra of the nanostructure can be modulated effectively by changing the size or shape of the series of metal bars. The results found can be useful in the design of novel optical device.

Preheating-temperature effect on structural and photoluminescent properties of sol–gel derived ZnO thin films

We investigated the evolution of structural and low-temperature photoluminescence properties of sol–gel derived ZnO thin films, as a function of pre-heating temperature between 300°C and 600°C. The pre-heating crystallization plays an important role in the lineshape of PL spectra. The increase in pre-heating temperature enables rearrangement of atoms at the pre-heating stage, leading to c-axis oriented growth of films, modification in lineshape of impurity-defect emission, and reduction of deep-level emission intensity.

Stark broadening data for spectral lines of rare-earth elements: Nb III

The electron-impact widths for 15 doubly charged Nb ion lines have been theoretically determined by using the modified semiempirical method. Using the obtained results, we considered the influence of the electron-impact mechanism on line shapes in spectra of chemically peculiar stars and white dwarfs.

High-Q Photonic Crystal Cavity in a Single-Mode Silicon Ridge Waveguide

We demonstrate experimentally a high-Q one-dimensional photonic crystal cavity in a widely-used 450 × 220nm single mode silicon ridge waveguide. Transmission spectrum measurement is performed by using the vertical fiber-grating coupling characterization method. The Q factor up to 2.6 × 104 is found by fitting the line shape of the transmission spectrum, and the normalized transmission of nearly 20% is achieved. Three-dimensional finite difference time domain calculations show that the modal volume of the fundamental mode is 1.1(λ/n)3. With the standard silicon waveguide width, the demonstrated 1D PhC cavity may be used as a building block for integrated photonic circuits and on-chip sensing applications.

Measuring the orientation of taurine in the active site of the non-heme Fe(II)/α-ketoglutarate-dependent taurine hydroxylase (TauD) using electron spin echo envelope modulation (ESEEM) spectroscopy.

The position and orientation of taurine near the non-heme Fe(II) center of the α-ketoglutarate (α-KG)-dependent taurine hydroxylase (TauD) was measured using Electron Spin Echo Envelope Modulation (ESEEM) spectroscopy. TauD solutions containing Fe(II), α-KG, and natural abundance taurine or specifically deuterated taurine were prepared anaerobically and treated with nitric oxide (NO) to make an S = 3/2 {FeNO}(7) complex that is suitable for robust analysis with EPR spectroscopy. Using ratios of ESEEM spectra collected for TauD samples having natural abundance taurine or deuterated taurine, (1)H and (14)N modulations were filtered out of the spectra and interactions with specific deuterons on taurine could be studied separately. The Hamiltonian parameters used to calculate the amplitudes and line shapes of frequency spectra containing isolated deuterium ESEEM were obtained with global optimization algorithms. Additional statistical analysis was performed to validate the interpretation of the optimized parameters. The strongest (2)H hyperfine coupling was to a deuteron on the C1 position of taurine and was characterized by an effective dipolar distance of 3.90 ± 0.25 Å from the {FeNO}(7) paramagnetic center. The principal axes of this C1-(2)H hyperfine coupling and nuclear quadrupole interaction tensors were found to make angles of 26 ± 5 and 52 ± 17°, respectively, with the principal axis of the {FeNO}(7) zero-field splitting tensor. These results are discussed within the context of the orientation of substrate taurine prior to the initiation of hydrogen abstraction.

Intersubband Absorption in Terahertz Lasers Based on Optically Pumped Quantum Well Structures

We study the effects of microscopic dynamics of electrons on the intersubband optical absorption in terahertz lasers based on optically pumped quantum wells (THz-OPQW). The ensemble Monte Carlo method is used to include different electron scattering mechanisms in the calculation, so that the dependence of intersubband absorption lineshape on microscopic dynamics of electrons can be easily investigated. We find that electron-electron scattering is the dominant factor to determine the absorption linewidth. The real distributions of hot electrons are included to study the temporal changes of the spectra lineshape. Our findings show that the dependence of spectral lineshape on electron population essentially results from the electron scattering and the non-Fermi electron energy distribution.

Analytical Study of Polarization Spectroscopy for the Jg=0 → Je=1 Transition

This work presents a theoretical study on the analytical calculation of the lineshape of polarization spectroscopy (PS) for the transition line 5s2 1S0 → 5s5p1P1 of 88Sr. From the obtained analytical form of the PS spectrum, we were able to identify how the saturation affected the lineshape of the PS spectrum. The results obtained will be useful for polarization spectroscopy experiments using the alkaline-earth atoms such as Sr or Yb.

Intermolecular/Interionic Vibrations of 1-Methyl-3-n-octylimidazolium Tetrafluoroborate Ionic Liquid and Benzene Mixtures

Intermolecular/interionic vibrational spectra of mixtures composed of 1-methyl-3-n-octylimidazolium tetrafluoroborate ionic liquid and benzene at mole fractions of 0 (i.e., neat ionic liquid), 0.2, 0.4, 0.6, 0.8, and 1.0 (i.e., neat benzene) have been investigated using femtosecond Raman-induced Kerr effect spectroscopy. The line shape of the low-frequency Kerr spectra obtained from Fourier transform analyses of the Kerr transients is strongly dependent on the composition of the mixture. By comparing the experimental spectra to calculated spectra based on experimental spectra of the neat liquids, it is evident that the spectrum is not achieved by simply combining those of the neat liquids and taking the mole fraction into consideration. Close examination of the spectral comparison results in a microscopic picture involving specific stacking of imidazolium and benzene rings that is not sufficiently stable to affect the ring librations. The quantum chemistry calculation results also support this proposal. No clear correlation between the first moment of the spectrum and the bulk parameter (i.e., the square root of the surface tension divided by the liquid density), which occurs for neat liquids, is evident.