Complete Absorption Spectra Research Articles

Dispersive x-ray absorption spectroscopy for time-resolved in situ monitoring of mechanochemical reactions.

X-ray absorption spectroscopy (XAS) provides a unique, atom-specific tool to probe the electronic structure of solids. By surmounting long-held limitations of powder-based XAS using a dynamically averaged powder in a Resonant Acoustic Mixer (RAM), we demonstrate how time-resolved in situ (TRIS) XAS provides unprecedented detail of mechanochemical synthesis. The use of a custom-designed dispersive XAS (DXAS) setup allows us to increase the time resolution over existing fluorescence measurements from ∼15minto 2s for a complete absorption spectrum. Hence, we here establish TRIS-XAS as a viable method for studying mechanochemical reactions and sampling reaction kinetics. The generality of our approach is demonstrated through RAM-induced (i) bottom-up Au nanoparticle mechanosynthesis and (ii) the synthesis of a prototypical metal organic framework, ZIF-8. Moreover, we demonstrate that our approach also works with the addition of a stainless steel milling ball, opening the door to using TRIS-DXAS for following conventional ball milling reactions. We expect that our TRIS-DXAS approach will become an essential part of the mechanochemical tool box.

Quantum chemical computation and spectroscopic investigation on antiviral drug Acyclovir:-In-silico and in-vitro analysis

In this researchwork, the complete vibrational features and electronic absorption spectra of antiviral drug Acyclovir were spectroscopically outlined and computationally explored by a combination of DFT (Density Functional Theory) calculations and Molecular docking process.A comparison between the simulated and experimentally gained spectra by FT-IR and FT-Raman showed concurrence.NBO analysis clearly confirms the evidence of intramolecular charge transfer in the guanine ring which enhances the bioactivity of the molecule. Natural Population analysis reveals that natural charges are responsive to the changes in the molecular structure of Acyclovir.Further HOMO-LUMO energy gap, electronegativity (ε),chemical potential (μ),global hardness (η),softness (σ) have been calculated. Also high value of electrophilicity index (ω) indicates high chemical stability of the molecule. Third order nonlinear optical parameters of Acyclovir were measured using closed and open aperture Z-scan technique to check the potential of the molecule to be an NLO material. Hirshfeld surface analysis and the 2D fingerprint plots revealed that H...H and O...H interactions are most prevalent. The molecular docking study enlightens the scope of using Acyclovir as an anticancer drug and its cytotoxicity in lung cancer cell is confirmed through MTT assay.

Synthesis, physicochemical properties and third-order optical nonlinearities of cadmium (II) dibromide l - Proline monohydrate for optical limiting application

Metal-semi organic NLO single crystal of Cadmium (II) dibromide l - Proline monohydrate (CBLPM) has been synthesized and the crystal was grown from solution by room temperature slow evaporation method. The crystal structure and cell parameters were refined by Rietveld refinement technique and confirmed that the metal-semi organic samples are in the orthorhombic system with space group P212121. The crystal structure of CBLPM is stabilized by intermolecular N–H…O, N–H….Br, O–H….O and O–H….Br hydrogen bonds. The water molecules serve as donors for the weak O–H⋯O and O–H⋯Br hydrogen bonds which link adjacent chains forming a three-dimensional structure. A Hirshfeld surface analysis suggests that the most significant contribution to the crystal packing is by H⋯Br contacts (26.2%). The complete vibrational features and electronic absorption spectra of the title compound were analyzed by FT-IR, FT-Raman and UV–visible spectra combined with density functional theory and time-dependent density functional computations. The second-order hyperpolarizability value of the molecule was also calculated at density functional theory method. The third-order nonlinear optical properties of the crystal were studied by Z-scan techniques using CW laser with wavelength 532 nm. The open aperture result exhibits the saturation absorption, which indicates that this material has potential candidate for optical limiting applications.

Large regional shortwave forcing by anthropogenic methane informed by Jovian observations.

Recently, it was recognized that widely used calculations of methane radiative forcing systematically underestimated its global value by 15% by omitting its shortwave effects. We show that shortwave forcing by methane can be accurately calculated despite considerable uncertainty and large gaps in its shortwave spectroscopy. We demonstrate that the forcing is insensitive, even when confronted with much more complete methane absorption spectra extending to violet light wavelengths derived from observations of methane-rich Jovian planets. We undertake the first spatially resolved global calculations of this forcing and find that it is dependent on bright surface features and clouds. Localized annual mean forcing from preindustrial to present-day methane increases approaches +0.25 W/m2, 10 times the global annualized shortwave forcing and 43% of the total direct CH4 forcing. Shortwave forcing by anthropogenic methane is sufficiently large and accurate to warrant its inclusion in historical analyses, projections, and mitigation strategies for climate change.

Z-scan measurements of the third-order optical nonlinearities and vibrational spectral studies by DFT computations on azo dye 1-(2-Methylphenylazo)-2-napthol

The nonlinear optical properties of azo dye 1-(2-Methylphenylazo)-2-napthol have been studied. The complete vibrational features and electronic absorption spectra of the title compound were analyzed by FT-IR, FT-Raman and UV–visible spectra combined with density functional theory and time-dependent density functional computations respectively. Nonlinear optical behavior was investigated by calculating the second-order hyperpolarizablity at DFT level. Third-order nonlinear optical parameters of 1-(2-Methylphenylazo)-2-napthol were measured using closed and open aperture Z-scan technique. The Z-scan result confirms, the dye exhibit self-focusing effect and the sign of the refractive nonlinearity is positive. The nonlinear refractive index (n2), nonlinear absorption coefficient (β), real and imaginary parts of third-order susceptibility (χ (3)) and second-order hyperpolarizability (γ) are calculated. The calculated results indicated that 1-(2-Methylphenylazo)-2-napthol have potential applications in optoelectronics and photonics.

Parameterization of the light absorption properties of chromophoric dissolved organic matter in the Baltic Sea and Pomeranian lakes

Abstract. This study presents three alternative models for estimating the absorption properties of chromophoric dissolved organic matter aCDOM(λ). For this analysis we used a database containing 556 absorption spectra measured in 2006–2009 in different regions of the Baltic Sea (open and coastal waters, the Gulf of Gdańsk and the Pomeranian Bay), at river mouths, in the Szczecin Lagoon and also in three lakes in Pomerania (Poland) – Obłęskie, Łebsko and Chotkowskie. The variability range of the chromophoric dissolved organic matter (CDOM) absorption coefficient at 400 nm, aCDOM(400), lay within 0.15–8.85 m−1. The variability in aCDOM(λ) was parameterized with respect to the variability over 3 orders of magnitude in the chlorophyll a concentration Chl a (0.7–119 mg m−3). The chlorophyll a concentration and aCDOM(400) were correlated, and a statistically significant, nonlinear empirical relationship between these parameters was derived (R2 = 0.83). On the basis of the covariance between these parameters, we derived two empirical mathematical models that enabled us to design the CDOM absorption coefficient dynamics in natural waters and reconstruct the complete CDOM absorption spectrum in the UV and visible spectral domains. The input variable in the first model was the chlorophyll a concentration, and in the second one it was aCDOM(400). Both models were fitted to a power function, and a second-order polynomial function was used as the exponent. Regression coefficients for these formulas were determined for wavelengths from 240 to 700 nm at 5 nm intervals. Both approximations reflected the real shape of the absorption spectra with a low level of uncertainty. Comparison of these approximations with other models of light absorption by CDOM demonstrated that our parameterizations were superior (bias from −1.45 to 62 %, RSME from 22 to 220 %) for estimating CDOM absorption in the optically complex waters of the Baltic Sea and Pomeranian lakes.

Demonstration of temperature imaging by H_2O absorption spectroscopy using compressed sensing tomography

This paper introduces temperature imaging by total-variation-based compressed sensing (CS) tomography of H2O vapor absorption spectroscopy. A controlled laboratory setup is used to generate a constant two-dimensional temperature distribution in air (a roughly Gaussian temperature profile with a central temperature of 677 K). A wavelength-tunable laser beam is directed through the known distribution; the beam is translated and rotated using motorized stages to acquire complete absorption spectra in the 1330-1365 nm range at each of 64 beam locations and 60 view angles. Temperature reconstructions are compared to independent thermocouple measurements. Although the distribution studied is approximately axisymmetric, axisymmetry is not assumed and simulations show similar performance for arbitrary temperature distributions. We study the measurement error as a function of number of beams and view angles used in reconstruction to gauge the potential for application of CS in practical test articles where optical access is limited.

The complete absorption spectra of InAs0.87Sb0.13 films grown by liquid phase epitaxy

We design, fabricate and characterize the InAs0.87Sb0.13 film with cutoff wavelength of 4.6μm on InAs (100) substrate, which is widely used as active layer of the multilayer device architecture for mid-infrared device used for the monitoring of carbon monoxide at 4.6μm. In order to accommodate the large lattice mismatch between the InAs0.87Sb0.13 epilayer and the InAs substrate, the InAs0.92Sb0.08 buffer layer was introduced. We acquired the complete absorption spectra and subsequently derived the basic parameters of InAs0.87Sb0.13 film and InAs0.92Sb0.08 buffer layer about absorption coefficient, optical energy band gap and the characteristic energy of Urbach edge from the Fourier transform infrared (FTIR) transmission spectra, which are very useful for modeling and simulation in the devices design.

Band to band optical absorption in LPE-growth InAs0.94Sb0.06 film

InAs1−xSbx films with x=0.06 were grown on InAs (100) substrates by liquid phase epitaxy (LPE). Different purification procedures were applied to get InAsSb samples with different carrier concentration. The complete optical absorption spectra including absorption edge and intrinsic absorption region of InAsSb samples were extracted from the room temperature transmission spectra. The energy band gaps of InAsSb samples were obtained by fitting the intrinsic absorption spectra, giving rise to the values of 303.4–305.1meV. The reciprocal slope (Eo) of the absorption edge related to the carrier concentration was also determined. The Eo value decreases with decrease of InAsSb epilayer carrier concentration.

Spatially resolved monitoring of adhesive application

When gluing wooden surfaces or particles that are to be pressed into particleboards, there is always the question of how one can measure the distribution of the adhesive during the process. New imaging techniques enable this by recording a complete absorption spectrum (hyperspectral image) for each pixel of the respective surface.

Optical investigation of the metal-insulator transition in FeSb2

We present a comprehensive optical study of the narrow gap $FeSb_2$ semiconductor. From the optical reflectivity, measured from the far infrared up to the ultraviolet spectral range, we extract the complete absorption spectrum, represented by the real part $\sigma_1(\omega)$ of the complex optical conductivity. With decreasing temperature below 80 K, we find a progressive depletion of $\sigma_1(\omega)$ below $E_g\sim 280$ cm$^{-1}$, the semiconducting optical gap. The suppressed (Drude) spectral weight within the gap is transferred at energies $\omega>E_g$ and also partially piles up over a continuum of excitations extending in the spectral range between zero and $E_g$. Moreover, the interaction of one phonon mode with this continuum leads to an asymmetric phonon shape. Even though several analogies between $FeSb_2$ and $FeSi$ were claimed and a Kondo-insulator scenario was also invoked for both systems, our data on $FeSb_2$ differ in several aspects from those of $FeSi$. The relevance of our findings with respect to the Kondo insulator description will be addressed.

Magneto-Optical Evidence of Double Exchange in a Percolating Lattice

Substituting Eu by Ca in ferromagnetic EuB6 leads to a percolation limited magnetic ordering. We present and discuss magneto-optical data of the Eu(1-x)Ca(x)B6 series, based on measurements of the reflectivity R(omega) from the far infrared up to the ultraviolet, as a function of temperature and magnetic field. Via the Kramers-Kronig transformation of R(omega) we extract the complete absorption spectra of samples with different values of x. The change of the spectral weight in the Drude component by increasing the magnetic field agrees with a scenario based on the double-exchange model, and suggests a crossover from a ferromagnetic metal to a ferromagnetic Anderson insulator upon increasing Ca content at low temperatures.

Cavity ringdown spectrum of the forbidden ÃE″2←X̃A2′2 transition of NO3: Evidence for static Jahn–Teller distortion in the à state

The Jahn-Teller effect in the first two excited states of the nitrate radical NO3 has yet to be experimentally elucidated. In this paper, direct evidence of strong Jahn-Teller interactions in the A state is presented from the first complete absorption spectrum of the A2E'' <-- X2A(2)' transition of NO3 in the gas phase in the region 5900-9000 cm(-1), at moderate resolution (0.15 cm(-1)). The observed spectrum is consistent with Herzberg-Teller selection rules, and reveals strong linear and quadratic Jahn-Teller interactions in the A state. Several of the vibronic bands have been tentatively assigned, including nu2, nu3, an irregular progression in nu4, and combination bands involving nu1. Our assignments are consistent with the previous works of Weaver et al. [A. Weaver, D. W. Arnold, S. E. Bradforth, and D. M. Neumark, J. Chem. Phys. 94, 1740 (1991)] and Hirota et al. [E. Hirota, T. Ishiwata, K. Kawaguchi, M. Fujitake, N. Ohashi, and I. Tanaka, J. Phys. Chem. 107, 2829 (1997)] The band origin is not observed, in accord with the selection rules, but is determined to be T0=7064 cm(-1) from the observation of the 4(1)0 hot band at 6695.7 cm(-1). Rotational contour analysis of this band indicates that the upper state is an asymmetric rotor, establishing that NO3 undergoes static Jahn-Teller distortion in the ground vibrational level of the A state.

Monitoring of fast transformations in solid state chemistry and heterogeneous catalysis by QEXAFS in the second scale

The present paper points out the possibility of investigating solid-solid transformations using time dependent x-ray absorption spectroscopy (QEXAFS) on a second scale. For this purpose, new crystal driving mechanics were developed which enable the measurement of complete x-ray absorption spectra extending over up to 2000 eV with repetition frequencies of up to 40 Hz and the possibility of monitoring a reference sample simultaneously. This permits to detect even very small changes of the edge position—and thus the chemical valency of the species of interest—with a high accuracy. The application of the new set up is demonstrated for the in situ analysis of the thermal decomposition of Co-oxalate-hydrate in different gas atmospheres. The results prove that the details of the decomposition process and the formed reaction products depend sensitively on the composition of the gas atmosphere.

Vibrational spectroscopy of large water clusters of known size

The structure of large water clusters of known size distributions 〈n〉 = 20-2000 is investigated by vibrational spectroscopy of the OH stretch mode. The water clusters are predissociated by a pulsed tunable infrared optical parametrical oscillator (OPO) in the frequency range 2800-3800 cm-1. Their fragments are detected off-axis by electron impact ionization and mass analyzed by a quadrupole mass spectrometer. The largest ion signal stems from the neutral water hexamer fragment. The ion yield is investigated at certain wavelengths while the size of the clusters is varied, and for certain sizes complete absorption spectra of the OH stretch motion are measured. Fingerprints of the different coordination types of the water molecules in the clusters are found and it turns out that our method is especially sensitive to amorphous structures with frequencies shifting in the range of 3300-3400 cm-1.

Effect of frequency redistribution in X-ray laser modeling

Calculations are presented of the spectral emissivity corrected for higher-order processes such as photon scattering. Usually, photon scattering is taken into account by postulating a complete frequency redistribution approximation, i.e., same absorption and emission spectra. However, cases exist in hot and dense plasmas for which partial frequency redistribution and angular redistribution play an important role for the radiative transfer mechanisms. Examples of X-ray lasers based on neon-like germanium ion emitters and hydrogen-like carbon ion emitters are considered.

Optical absorption spectra of the Holstein molecular crystal for weak and intermediate electronic coupling

We investigate the optical absorption spectrum in a Holstein model for a molecular chain with Frenkel excitons and linear coupling to one internal vibration. The model is extended for nearest-neighbor charge-transfer excitons that mix with the Frenkel excitons. We represent the Hamiltonian in a displaced oscillator (Lang-Firsov) basis and employ a problem-adapted scheme for the truncation of the phonon basis. For weak and intermediate electronic coupling, the complete absorption spectrum and the structure of the relevant eigenstates become accessible by direct numerical diagonalization. We discuss the structure of the phonon clouds and the applicability of the molecular vibron model, in which only joint exciton-phonon configurations are included. As examples, we model absorption spectra of PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) and MePTCDI $(N\ensuremath{-}{N}^{\ensuremath{'}}$-dimethylperylene-3,4,9,10-dicarboximide).

Analysis of Charge-Transfer Complex Absorption Spectra and the Applicability of the Mulliken two-State Model

Complete absorption spectra, free from interference due to an unbound acceptor and donor, of several charge-transfer complexes have been examined. These spectra serve as a significant test to the applicability of the Mulliken two-state model for this series of complexes. the appearance of multiple new absorption bands and the trend in the observed oscillator strength of the CT transitions and the localized excitation within the complex spectrum require significant expansions of Mulliken's simple two-state model. Multiple new CT absorption bands are frequently encountered and their appearance has been explained in terms of multiple ion-pair states participating in CT interactions. the relative positions of these bands are predicted based on the gas-phase ionization potentials of the donors and the electron affinity of the acceptor in excellent agreement with the observed spectra achieved. the integrated absorption intensities of the localized bands within each CT complex spectrum have been measured and used as an indicator of the extent on intensity borrowing by the CT transition. These measurements show that for the better donors used in this study, i.e. hexamethylbenzene and pentamethylbenzene, intensity borrowing is not significant. However, for the poorer donors used, an increasing contribution of the LE within the CT absorption bands is observed. a multi-state model, which includes the localized excited state of the acceptors well as additional ion-pair states, is the minimum required to describe these complexes.

Feasibility tests of transmission x-ray photoelectron emission microscopy of wet samples

We performed feasibility tests of photoelectron emission spectromicroscopy of wet samples in the water window (285–532 eV) soft x-ray spectral region. Water was successfully confined in an ultrahigh vacuum compatible compartment with x-ray transparent sides. This water cell was placed in the MEPHISTO spectromicroscope in a transmission geometry, and complete x-ray absorption spectra of the water window region were acquired. We also show micrographs of test samples, mounted outside of the compartment, and imaged through the water. This technique can be used to study liquid chemistry and, at least to the micron level, the microstructure of wet samples. Possibilities include cells in water or buffer, proteins in solution, oils of tribological interest, liquid crystals, and other samples not presently accessible to the powerful x-ray photoelectron emission spectromicroscopy technique.

Structural and optical properties of small oxygen-doped- and pure-silver clusters

We present calculations of absorption patterns in large energy intervals for the stable structures of oxygen-doped- and pure-silver clusters using the linear-response-type approach which allows one to correlate all 11 and 6 electrons per Ag and O atoms, respectively. For this purpose, we designed a new 11-electron relativistic effective core potential (11e–RECP) for Ag atoms at the correlated level of theory, which, together with the associated AO basis set, provide an accurate description of excited states. This has been evidenced by the comparison of our results with available experimental data. We found that inclusion of d electrons in the RECP, as well as in the correlation treatment, is important for an accurate prediction of the complete absorption spectra. Moreover, the influence of d electrons of Ag atoms becomes pronounced, even for structural properties of AgnO clusters. Also, the electrons of oxygen are strongly involved in excitations besides those of Ag-valence electrons, leading to intense transitions spread in a large energy interval. The role O plays in Ag n O clusters differs substantially from the one it plays in oxygen-doped alkali clusters, because of the participation of the d electrons of Ag atoms.