Lorentzian Band Research Articles

Infrared ellipsometry study of the charge dynamics in K3p -terphenyl

We report an infrared ellipsometry study of the charge carrier dynamics in polycrystalline ${\mathrm{K}}_{x}p$-terphenyl samples with nominal $x=3$, for which signatures of high-temperature superconductivity were previously reported. The infrared spectra are dominated by two Lorentzian bands with maxima around 4000 and $12 000 {\mathrm{cm}}^{\ensuremath{-}1}$ which, from a comparison with calculations based on a H\"uckel model, are assigned to intramolecular excitations of $\ensuremath{\pi}$ electrons of the anionic $p$-terphenyl molecules. The intermolecular electronic excitations are much weaker and give rise to a Drude peak and a similarly weak Lorentzian band around $220 {\mathrm{cm}}^{\ensuremath{-}1}$. A dc resistivity of about $0.3 \mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$ at $300\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ is deduced from the IR data, comparable to values measured by electrical resistivity on a twin sample. The analysis of the temperature dependence of the low-frequency response reveals a gradual decrease of the plasma frequency and the scattering rate of the Drude peak below $300\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ that gets anomalously enhanced below $90\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The corresponding missing spectral weight of the Drude peak appears blueshifted towards the Lorentz band at $220 {\mathrm{cm}}^{\ensuremath{-}1}$. This characteristic blueshift signifies an enhanced localization of the charge carriers at low temperatures and contrasts the behavior expected for a bulk superconducting state for which the missing spectral weight would be redshifted to a delta function at zero frequency that accounts for the loss-free response of the superconducting condensate. Our data might still be compatible with a filamentary superconducting state with a volume fraction well below the percolation limit for which the spatial confinement of the condensate can result in a plasmonic resonance at finite frequency.

In-situ study on structure evolution and gasification reactivity of biomass char with K and Ca catalysts at carbon dioxide atmosphere

The structural evolution and gasification reactivity of biochar prepared from the pyrolysis of wheat straw were investigated by in-situ Raman spectroscopy and thermogravimetric analysis. The Raman spectra consisted of a combination of four Lorentzian bands (D1, D2, D4, G) and one Gaussian band (D3) in the first-order region. The experimental results showed that the addition of catalysts or the presence of ash could improve the CO2 gasification reactivity of biochar and result in a larger ID1/IG ratio and a lower IG/IALL ratio, meaning that the carbon structure was less ordered, and there were also more active sites such as amorphous carbon and cross-linked structures; Ca-based catalysts and K-based catalysts changed the evolution of biochar structure in a different way in CO2 atmosphere, the ID3/ID1 of Ca-based biochar was close to the value of non-catalyst biochar and decreased slowly, indicating that the Ca-based catalysts can stabilize the aromatic rings, while the IG/IALL of K-based biochar decreases significantly and the ID3/ID1 increased significantly, indicating the increase of carbon structure defects and the cracking of large aromatic rings in bio-char into small ones; a scheme of K and Ca reaction with biochar in CO2 gasification process was proposed.

Dual-frequency comb spectroscopy studies of ionic strength effects in time-resolved ATR-SEIRAS

• DFCS allows sub-millisecond resolution of temporal processes occurring at an electrode surface. • IR transient time constants are directly proportional to the RC cell constant. • Absorption spectra line shape depends on coverage. Attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies of the potential induced desorption/adsorption of a model organic monolayer is described using a paradigm-challenging dual frequency comb spectrometer. Experimentally measured ATR-SEIRAS transients reveal that both the rates of adsorption and desorption of 4-dimethylaminopyridine (DMAP) are dependent on the ionic strength of the supporting electrolyte. The characteristic time scales of monolayer desorption are found to be directly proportional to the spectroelectrochemical cell time constant indicating that the rate of film dissolution is much faster than the RC charging of the interface. The slow response of the interfacial charging process relative to the kinetics of the film re-organization/desorption processes means that the transient is parametrically linked to the potential dependent DMAP adsorption isotherm. The transients also reveal that the line shape of the molecular IR absorption feature exhibits a temporal dependence. A Lorentzian band is seen at early stages of the desorption transient but increasingly exhibit an anomalous bimodal line-shape at longer times. The development of the anomalous line shape is more pronounced at equivalent times in higher ionic strength electrolytes. Such an effect has been modelled using effective medium theory and is explained by the fact that the fraction of organic layer in the SEIRAS active film influences the observed apparent absorption features. The observation of a coverage dependence on SEIRAS line shapes adds new complexity to previous reports that linked anomalous absorption features exclusively to the metal film morphology and metal volume fraction.

In Situ Raman Spectroscopy Study on Catalytic Pyrolysis of a Bituminous Coal

How different catalysts would affect the evolution of char structure with increasing temperature during the pyrolysis of coal is fundamentally important for the clean utilization of coal. In this study, we applied in situ Raman spectroscopy and a fixed-bed reactor to characterize the evolution of char structure and product gas formation behavior. The results showed that the formation curves of the main gases presented two stages and the catalyst enhanced the pyrolysis significantly. The Raman spectra were fitted with a combination of four Lorentzian bands (D1, D2, D4, G) and one Gaussian band (D3) in the first-order region. Spectral parameters, such as band position, full widths at half-maximum (FWHM), and band area ratio, were used to characterize char structure. The D1 and G band FWHM and band area ratios ID1/IG, ID3/IG, and ID4/IG increased with increasing temperature, while the D1 and G band positions and IG/IAll decreased, indicating a decrease in the ordering of the char structure. The addition of c...

Femtosecond Time-Resolved Dynamics of trans-Azobenzene on Gold Nanoparticles.

We report a first femtosecond time-resolved transient absorption study of the photoinduced ultrafast dynamics of trans-azobenzene (AB) on gold nanoparticles (AuNPs). The observed changes in optical density following excitation at λ = 357 nm were analyzed by using temperature-dependent Mie theory and by Lorentzian band fitting to disentangle the ultrafast relaxation of the local surface plasmon resonance (LSPR) excitation of the Au core and the electronic deactivation of the attached AB ligands. The analysis of the dynamics associated with the AB photochrome yielded lifetime constants of τ1 = 1.2 ± 0.2 ps and τ2 = 4.7 ± 1.1 ps. Both values together indicate surprisingly little difference in the dynamics of the AB ligand on the AuNPs vs in solution. Our results thus highlight the extraordinarily efficient electronic decoupling of the azo chromophore and the Au core by the alkyl linker chain.

Influences of magmatic intrusion on the macromolecular and pore structures of coal: Evidences from Raman spectroscopy and atomic force microscopy

Magmatic intrusion into coal-bearing sequences can significantly affect the rank of the intruded coal and change the macromolecular and pore structures. Here, we use Raman microscope and Atomic force microscope (AFM) to obtain quantitative information on these transformations. Six coal samples of different ranks taken from a magmatic intrusion zone of Huainan Coalfield, China, were studied. The Raman spectra were fitted with a combination of 8 Lorentzian bands and 1 Gaussian band. We found that the macromolecular structures in coals of different ranks have significant relationships with Raman spectral parameters, particularly the band area ratios (ID1/IG, ID2/IG, ID3/IG, ID4/IG and IG/IAll). With the increase of coal rank, ID1/IG, ID2/IG, ID3/IG and ID4/IG show trends of decreasing intensity, suggesting an enhanced orientation of aromatic hydrocarbons. Observations by Atomic force microscopy indicate that the pore parameters (e.g. amount, size, shape) are quite different for different ranks of coals. The pore size of low-rank bituminous coal is much larger than high-rank anthracite and pore abundance is higher in the former. In addition, there is also good correspondence between the surface topography of coal grains and coal rank.

Evaluation of Raman Parameters Using Visible Raman Microscopy for Soot Oxidative Reactivity

Soot crystalline structure was evaluated for four soot samples and one carbon black using Raman parameters obtained from first-order Raman spectra. For this work, different numbers of peaks from three to as many as five curves with combined Lorentzian and Gaussian bands were fitted for the spectra, and Raman parameters were compared with soot oxidative reactivity, in order to investigate the correlation between the Raman parameters and the oxidative reactivity for each curve-fitting method. Among these methods, the combination of three Lorentzian-shaped bands at about 1200 (D4), 1360 (D1), and 1580 cm–1 (G), and one Gaussian-shaped band at about 1500 cm–1 (D3), which is designated as 3L1G, shows the most consistent results for various Raman parameters with respect to soot oxidative reactivity; amorphous carbon fraction, crystallite size, and distribution of crystallite size are in good agreement with soot oxidative reactivity. Also, crystallite sizes from several empirical formulas using Raman spectroscop...

Attenuated total reflection spectroscopy under conditions of weak absorption: Further development of a new method for determination of integrated intensities

Development of a new method for the determination of the integrated intensities in isotropic condensed media is suggested. In a previous publication, with the use of analytical calculations, it is shown that, for the ATR spectra measured under conditions of weak absorption, the area under the absorbance curve of an isolated Lorentzian band is directly proportional to the integrated intensity of this band. It is also shown that the proportionality coefficient between these two parameters contains only one unknown parameter: the real part of the complex dielectric constant for the studied medium at the maximum of the studied band. In order to determine the numerical value of this parameter and, at the same time, to find the integrated intensity value, it is suggested to carry out two experiments; in these experiments, the same band is studied while the most important parameters are varied, such as the IRE refractive index, the angle of incidence, and the polarization. The main random and systematic errors of the suggested method are considered: ways to minimize these errors are discussed. The approach developed in this work is compared with other methods for determination of the integrated intensities.

Char Structural Evolution during Pyrolysis and Its Influence on Combustion Reactivity in Air and Oxy-Fuel Conditions

Three kinds of Chinese coal and a biomass were pyrolyzed by N2 and CO2 in a bench scale fluidized bed reactor. Fourier transform (FT)-Raman/infrared (IR) spectroscopy was used to identify microstructure and to evaluate the structural evolution of chars generated in N2 and CO2 environments, which are the main diluting gases of air and oxy-fuel environments. The Raman spectra were fitted with five Lorentzian bands. The reactivities of the char were measured by a thermogravimetric analyzer from room temperature to 1373 K in air and oxy-fuel conditions with O2 concentration of 21%. The derived activation energy for different samples was correlated with the Raman structural parameters. Results showed that more disordered char was formed with the pyrolysis in CO2 than that in N2, and new O-containing functional structures would be introduced into the char structure in CO2 atmosphere. The char structures became less ordered as the sample rank decreased. The reactivity of CO2 char was higher than that of N2 char,...

Relationship between Infrared Peak Maximum Position and Molecular Interactions

The Procter & Gamble Company, West Chester, Ohio 45069, USAReceived August 3, 2011, Accepted September 15, 2011We explored the interpretation of the well-accepted correlation between the apparent peak maximum positionshift and extent of molecular interactions, like hydrogen bonding and dipole-dipole interactions, based on theoverlapped multiple band model. The simulation of two overlapped Lorentzian bands was carried out tointerpret how the maximum position of a composite peak relates to the relative contributions of two speciesrepresenting the different levels of molecular interactions, i.e., free (or very weekly bound) vs. strongly bound.To demonstrate the validity of our interpretation of the origin of the peak position shift, the temperature-dependent IR spectra of ethylene glycol were also analyzed. It was found through the analysis of simulated andexperimental spectra that the apparent peak shift in certain case can be safely interpreted as the measure of thestrength of hydrogen bonding. The result of this study gives a new insight to interpret molecular interactionsprobed by vibrational spectroscopy. Key Words : Frequency shifts, Overlapped bands, Self-modeling curve resolution (SMCR), Hydrogen bond-ing, Molecular interactionIntroductionThe extent of bathochromic shift of certain IR peaks underthe influence of temperature or solution composition hasbeen historically used as a convenient metric to characterizethe degree or strength of specific molecular interactions,such as hydrogen bonding and dipole-dipole interactions.Pimentel and Sederholm published a classical paper on the“empirical correlation” between shift of stretching fre-quencies and hydrogen bond distances in solid crystals.

Method of Spectral Subtraction of Gas-Phase Fourier Transform Infrared (FT-IR) Spectra by Minimizing the Spectrum Length

A new method of spectral subtraction for gas-phase Fourier transform infrared (FT-IR) spectra was developed for long-path gas measurements. The method is based on minimization of the length of the spectrum that results from subtracting the spectrum of an individual component of a gas mixture (water, CO(2), etc.) from the experimental spectrum of the mixture. For this purpose a subtraction coefficient (k(min)) is found for which the length of the resulting spectrum is minimized. A mathematical simulation with two Lorentzian absorption bands was conducted and the limits of application for the proposed method were determined. Two experimental examples demonstrate that a successful result could be achieved in the case when the subtrahend spectrum contains a number of narrow absorption bands (such as the spectrum of water vapor).

Growth of Few Layers Graphene on Silicon Carbide from Nickel Silicide Supersaturated with Carbon

Few Layers Graphene (FLG) films were grown on the carbon-terminated surface of 4H-SiC from nickel silicide supersaturated with carbon. The process was realised by annealing of thin Ni films deposited on silicon carbide followed by wet processing to remove the nickel silicide. To identify and characterize the fabricated FLG films, micro-Raman scattering spectroscopy, AFM and optical microscopy have been used. The films grown on samples with initially deposited nickel thinner than 20 nm show clear graphene footprints in micro-Raman scattering spectra, namely a single component, Lorentzian shape 2D band with FWHM remarkably lower than that of the 2D peak of graphite.

Tuning the Kondo and Fano effects in double quantum dots

We demonstrate delicate control over the Kondo effect and its interplay with quantum interference in an Aharonov-Bohm interferometer containing one Kondo dot and one noninteracting dot. It is shown that the Kondo resonance undergoes a dramatic evolution as the interdot tunnel coupling progressively increases. A novel triple Kondo splitting occurs from the interference between constant and Lorentzian conduction bands that cooperate in forming the Kondo singlet. The device also manifests a highly controllable Fano-Kondo effect in coherent electronic transport, and can be tuned to a regime where the coupled dots behave as decoupled dots.

Spectral and temporal luminescent properties of Eu(III) in humic substance solutions from different origins

Although a high heterogeneity of composition is awaited for humic substances, their complexation properties do not seem to greatly depend on their origins. The information on the difference in the structure of these complexes is scarce. To participate in the filling of this lack, a study of the spectral and temporal evolution of the Eu(III) luminescence implied in humic substance (HS) complexes is presented. Seven different extracts, namely Suwannee River fulvic acid (SRFA) and humic acid (SRHA), and Leonardite HA (LHA) from the International Humic Substances Society (USA), humic acid from Gorleben (GohyHA), and from the Kleiner Kranichsee bog (KFA, KHA) from Germany, and purified commercial Aldrich HA (PAHA), were made to contact with Eu(III). Eu(III)-HS time-resolved luminescence properties were compared with aqueous Eu 3+ at pH 5. Using an excitation wavelength of 394 nm, the typical bi-exponential luminescence decay for Eu(III)-HS complexes is common to all the samples. The components τ 1 and τ 2 are in the same order of magnitude for all the samples, i.e., 40 ≤ τ 1 (μs) ≤ 60, and 145 ≤ τ 2 (μs) ≤ 190, but significantly different. It is shown that different spectra are obtained from the different groups of samples. Terrestrial extract on the one hand, i.e. LHA/GohyHA, plus PAHA, and purely aquatic extracts on the other hand, i.e., SRFA/SRHA/KFA/KHA, induce inner coherent luminescent properties of Eu(III) within each group. The 5D 0 → 7F 2 transition exhibits the most striking differences. A slight blue shift is observed compared to aqueous Eu 3+ ( λ max = 615.4 nm), and the humic samples share almost the same λ max ≈ 614.5 nm. The main differences between the samples reside in a shoulder around λ ≈ 612.5 nm, modelled by a mixed Gaussian–Lorentzian band around λ ≈ 612 nm. SRFA shows the most intense shoulder with an intensity ratio of I 612.5/ I 614.7 = 1.1, KFA/KHA/SRHA share almost the same ratio I 612.5/ I 614.7 = 1.2–1.3, whilst the LHA/GohyHA/PAHA group has a I 612.5/ I 614.5 = 1.5–1.6. This shows that for the two groups of complexes, despite comparable complexing properties, slightly different symmetries are awaited.

Comparison of the Raman spectra of ion irradiated soot and collected extraterrestrial carbon

We use a low pressure flame to produce soot by-products as possible analogues of the carbonaceous dust present in diverse astrophysical environments, such as circumstellar shells, diffuse interstellar medium, planetary disks, as well as in our own Solar System. Several soot samples, displaying an initial chemical diversity from aromatic to aliphatic dominated material, are irradiated with 200–400 keV H +, He +, and Ar ++ ions, with fluences comprised between 10 14 and 10 16 ions/cm 2, to simulate expected radiation induced modification on extraterrestrial carbon. The evolution of the samples is monitored using Raman spectroscopy, before, during, and after irradiation. A detailed analysis of the first- and second-order Raman spectra is performed, using a fitting combination of Lorentzian and/or Gaussian-shaped bands. Upon irradiation, the samples evolve toward an amorphous carbon phase. The results suggest that the observed variations are more related to vacancy formation than ionization processes. A comparison with Raman spectra of extraterrestrial organic matter and other irradiation experiments of astrophysically relevant carbonaceous materials is presented. The results are consistent with previous experiments showing mostly amorphization of various carbonaceous materials. Irradiated soots have Raman spectra similar to those of some meteorites, IDPs, and Comet Wild 2 grains collected by the Stardust mission. Since the early-Sun expected irradiation fluxes sufficient for amorphization are compatible with accretion timescales, our results support the idea that insoluble organic matter (IOM) observed in primitive meteorites has experienced irradiation-induced amorphization prior to the accretion of the parent bodies, emphasizing the important role played by early solar nebula processing.

Method for the Estimation of the Mean Lorentzian Bandwidth in Spectra Composed of an Unknown Number of Highly Overlapped Bands

We introduce a method for the estimation of the mean Lorentzian bandwidth of the component bands in a spectrum. The method is computationally simple, using only the module of the Fourier transform of the spectrum, and its first derivative. Moreover, the presented method does not require knowledge of the number of bands in the spectrum, their band positions, or their band areas. Furthermore, it works on spectra containing Lorentzian bands, as well as Gaussian and Voigtian bands. Therefore, the introduced method seems especially well suited for obtaining a representative Lorentzian width for highly overlapped bands, independent of their number and Lorentzian/Gaussian character. We describe how different experimental limitations (spectral truncation, offset error, presence of noise, etc.) may affect the performance of the method, and when required we propose effective alternatives to minimize their effects. Finally, we show the application of the method to an experimental spectrum: the amide I band of a dry film of the solubilized ADP/ATP carrier. The estimation of the mean Lorentzian width can allow, for instance, for a more objective selection of the deconvolution width in Fourier self-deconvolution, allowing for a more objective and reliable analysis of the amide I band of proteins. The mean Lorentzian width can also be useful to obtain an estimation of the homogenous broadening and vibrational relaxation of the amide I vibration of proteins, without requiring complex pump-probe experiments.

Vibrational Absorption and Circular Dichroism Studies of trans-(3S,4S)-d6-Cyclopentene in the Gas Phase

Vibrational absorption (IR) and circular dichroism (VCD) measurements of trans-(3S,4S)-d6-cyclopentene in the gas phase were performed in the C-H, C-D, and mid-infrared regions. In this study, we report the first VCD spectra recorded at high spectral resolution (up to 0.5 cm(-1)) with a very good signal-to-noise ratio (differential absorbance lower than 5 x 10(-6)). The quality of the experimental spectra allows us the observation of the vibration-rotation structure of the bands in both absorption and VCD spectra. Experimental spectra have been compared with the density functional theory (DFT) absorption and VCD spectra, calculated using B3LYP functional and cc-pVTZ basis set for the axial, equatorial, and planar conformers. Lorentzian and PQR band profiles have been used to convert the calculated dipolar and rotational strengths. In the mid-infrared (<2000 cm(-1)) region, predicted (population-weighted) spectra were in excellent agreement with experiment, allowing the determination of the absolute configuration of this molecule. Above 2000 cm(-1), a reasonable agreement was obtained even if anharmonicity was not considered and if Fermi resonance occurs in the C-D stretching region. Finally, a more precise analysis of the absorption spectrum has been achieved by taking into account anharmonicity of the C-H stretching and its coupling with the ring-puckering motion.

Char structure characterised by Raman spectroscopy and its correlations with combustion reactivity

Abstract Raman spectroscopy was applied to characterise the microstructure of coal chars generated under various heat treatment conditions, which was correlated with the combustion reactivity measured by thermogravimetric analysis. The Raman spectra were fitted with the combination of 4 Lorentzian bands and 1 Gaussian band. It was found that the increase of char microstructural order under heat treatment can be characterised by Raman parameters, in particular the band area ratios, indicated by the increase in IG/IAll and the decrease in ID1/IG, ID2/IG, ID3/IG and ID4/IG with increasing treatment temperature and/or time. The combustion reactivity of the chars from demineralised coals was found to have good correlations with the band area ratios, independent of coal type and heat treatment condition. It was found that the presence of inorganic matter in coal chars marginally affected the evolution of the average char microstructure. However, it did affect the char reactivity evolution. It was confirmed that the thermal deactivation of coal char during heat treatment was dependent not only on the ordering of char crystalline structure but also on the loss of catalytic activity of the inorganic matter.

Minimizing optical losses in bulk heterojunction polymer solar cells

The efficiency that a solar cell can reach is ultimately limited by the number of photons absorbed in its active layer. Bulk heterojunction polymer solar cells are fabricated from a stack of thin film layers, each of which is thinner than a single wavelength from an incident photon within its absorption band. One consequence of this thin film layer stack is a strong optical interference between the various layers that can change the quantity of light dissipated in the active layer by 50%. Here we use optical modeling to quantitatively calculate the dissipation in each of the various layers as functions of wavelength and layer thickness. Using this information the loss free short circuit current density can be calculated (Jscmax). Optimization of Jscmax leads to direct improvements in the efficiency of the solar cell through improved light dissipation in the active layer. The optical properties for a P3HT:PCBM active layer and a model Lorentzian low band gap spectrum are optimized and ideal fabrication conditions are reported for these materials.

Non-Markovian modification of the golden rule rate expression

The reformulation of the standard golden rule approach considered in this paper for treating reactive tunneling reduces the computation of the reaction rate to a derivation of band shapes for energy levels of reactant and product states. This treatment is based on the assumption that the medium environment is actively involved as a partner in the energy exchange with the reactive subsystem but its reorganization effect is negligible. Starting from the quantum relaxation equation for the density matrix, the required band shapes are represented in terms of the spectral density function, exhibiting the continuum spectrum inherent to the interaction between the reactants and the medium in the total reactive system. The simplest Lorentzian spectral bands, obtained under Redfield approximation, proved to be unsatisfactory because they produced a divergent rate expression at low temperature. The problem is resolved by invoking a refined spectral band shape, which behaves as Lorentzian one at the band center but decays exponentially at its tails. The corresponding closed non-Markovian rate expression is derived and investigated taking as an example the photochemical H-transfer reaction between fluorene and acridine proceeding in the fluorene molecular crystal. The kinetics in this reactive system was thoroughly studied experimentally in a wide temperature range [B. Prass et al., Ber. Bunsenges. Phys. Chem. 102, 498 (1998)].