Bolometric measurement of the far-infrared absorption spectrum of single-crystal tetrathiafulvalene-tetracyanoquinodimethane

The far-infrared absorption spectrum of single-crystal TTF-TCNQ has been measured with high resolution by using the crystal as a bolometric detector at 7 K. The spectrum contains weak lattice modes, stronger intra-molecular modes with splittings due possibly to electron-phonon interactions, a direct gap near 300 cm^?1, a possible indirect gap near 100 cm^?1, and a possible pinned Fröhlich mode at low energy.     

BH4− Induced far-infrared absorption in the phonon gap of KI

High resolution measurements of the far-infrared lattice gap modes due to BH₄^? in KI are reported. The observed bands at 85.45 ± 0.05 and 84.94 ± 0.05 cm^?1 are ascribed as resulting from the presence of two stable boron isotopes in the BH₄^? ion. The gap modes are calculated by allowing for the elastic relaxation of the lattice around the impurity. The results of a calculation for the Br^? gap modes in KI are also presented.     

Synthesis of Ge-Sn at high pressure and high temperature in a laser-heated diamond anvil cell

Ge–Sn compound is predicted to be a direct band gap semiconductor with a tunable band gap. However, the bulk synthesis of this material by conventional methods at ambient pressure is unsuccessful due to the poor solubility of Sn in Ge. We report the successful synthesis of Ge–Sn in a laser-heated diamond anvil cell (LHDAC) at ~7.6 GPa &; ~2000 K. In situ Raman spectroscopy of the sample showed, apart from the characteristic Raman modes of Ge TO (Г) and β-Sn TO (Г), two additional Raman modes at ~225 cm^?1 (named Ge–Sn₁) and ~133 cm^?1 (named Ge–Sn₂). When the sample was quenched, the Ge–Sn₁ mode remained stable at ~215 cm^?1, whereas the Ge–Sn₂ mode had diminished in intensity. Comparing the Ge–Sn Raman mode at ~225 cm^?1 with the one observed in thin film studies, we interpret that the observed phonon mode may be formed due to Sn-rich Ge–Sn system. The additional Raman mode seen at ~133 cm^?1 suggested the formation of low symmetry phase under high P–T conditions. The results are compared with Ge–Si binary system.     

The adsorption of ammonia on a Fe(110) single crystal surface studied by high resolution electron energy loss spectroscopy (EELS)

EELS spectra of ammonia adsorbed on a Fe(110) single crystal surface at 120 K reveal four different molecular adsorption states:1. At very low exposures (0.05 L) three vibrational losses at 345 cm^?1, 1170 and 3310 cm^?1 are observed which are attributed to the symmetric Fe-N stretching-, N-H₃ deformation and N-H₃ stretching modes of chemisorbed molecular ammonia, respectively. The observation of only three vibrational losses indicates an adsorption complex of high symmetry (C_3v).2. Further exposures up to 0.5 L cause the appearance of additional losses at 1450 cm^?1, 1640 cm^?1 and 3370 cm^?1. The latter two are interpreted as the degenerate NH₃ deformation and - stretching modes of molecularly adsorbed NH₃. The 1450 cm^?1 loss is a combination of the losses at 345 cm^?1 and 1105 cm^?1. The observation of 5 vibrational losses is consistent with an adsorption complex of C_s symmetry.3. In the exposure range from 0.5 to 2 L adsorption of molecular ammonia in a second layer is observed. This phase is characterized by a symmetric deformation mode at 1190 cm^?1 and by two additional very intense modes at 160 cm^?1 and 350 cm^?1 which are due to rotational and translational modes.4. Exposures above 2 L cause multilayer condensation of ammonia characterized by translational and rotational bands at 190 cm^?1, 415 cm^?1 and 520 cm^?1, and a symmetric deformation mode at 1090 cm^?1. A broad loss feature around 3300 cm^?1 is attributed to hydrogen bonding in the condensed layer.Thermal processing of a Fe(110) surface ammonia covered at 120 K leads to decomposition of the ammonia into hydrogen and nitrogen above 260 K. No vibrational modes due to adsorbed NH or HN₂ species were detected.     

Infrared spectrum and vibrational potential function of the chlorite anion in the matrix-isolated M+ClO2− species

The chlorite anion, ClO₂^?, was prepared for spectral investigation by depositing alkali metal atoms and chlorine dioxide at high dilution in argon onto a 15°K optical surface. Intense infrared absorptions near 820, 790, and 420 cm^?1, which exhibited small alkali metal effects, are due to the three intraionic modes of the chlorite anion in the M⁺ClO₂^? species. The ClO force constant for ClO₂^? (4.11 mdyn/Å) is less than the value for ClO₂ (6.61 mdyn/Å), which is consistent with the antibonding character of the additional electron on ClO₂^?.     

Spin distributions in the vibrational excitations of closed-shell nuclei

Self-consistent Hartree-Fock and RPA calculations with the Skyrme-type interaction SGII are used for a systematic investigation of the 1⁺ and the triplet 0^?, 1^?, 2^? states in ⁴⁰Ca and ²⁰⁸Pb. Response functions to spin-dependent multipole operators are calculated and the particle-hole structure of the spin-dependent collective states is studied. Collective spin-dependent 0^? and 1^? states above the giant dipole resonance as well as a collective spin-independent 2^? state (twist mode) are identified. Transition spin and current densities are calculated for the collective excitations and found to be useful for the study of these excitation modes.     

Removal of heavy metals from aqueous solutions using Fe3O4, ZnO, and CuO nanoparticles

This study investigated the removal of Cd²⁺, Cu²⁺, Ni²⁺, and Pb²⁺ from aqueous solutions with novel nanoparticle sorbents (Fe₃O₄, ZnO, and CuO) using a range of experimental approaches, including, pH, competing ions, sorbent masses, contact time, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The images showed that Fe₃O₄, ZnO, and CuO particles had mean diameters of about 50?nm (spheroid), 25?nm (rod shape), and 75?nm (spheroid), respectively. Tests were performed under batch conditions to determine the adsorption rate and uptake at equilibrium from single and multiple component solutions. The maximum uptake values (sum of four metals) in multiple component solutions were 360.6, 114.5, and 73.0?mg?g^?1, for ZnO, CuO, and Fe₃O₄, respectively. Based on the average metal removal by the three nanoparticles, the following order was determined for single component solutions: Cd²⁺?>?Pb²⁺?>?Cu²⁺?>?Ni²⁺, while the following order was determined in multiple component solutions: Pb²⁺?>?Cu²⁺?>?Cd²⁺?>?Ni²⁺. Sorption equilibrium isotherms could be described using the Freundlich model in some cases, whereas other isotherms did not follow this model. Furthermore, a pseudo-second order kinetic model was found to correctly describe the experimental data for all nanoparticles. Scanning electron microscopy, energy dispersive X-ray before and after metal sorption, and soil solution saturation indices showed that the main mechanism of sorption for Cd²⁺ and Pb²⁺ was adsorption, whereas both Cu²⁺ and Ni²⁺ sorption were due to adsorption and precipitation. These nanoparticles have potential for use as efficient sorbents for the removal of heavy metals from aqueous solutions and ZnO nanoparticles were identified as the most promising sorbent due to their high metal uptake.     

Laser-induced Raman scattering in calcium titanate

The Raman spectrum of polycrystalline calcium titanate prepared by a liquid mix technique and heated to 800°C has been recorded at room temperature using an argon-ion laser as exciter. The observed spectrum was interpreted on the basis of factor-group C_2V. Not all of the Raman active modes predicted by factor group analysis were observed and this could be due to: over-lapping of bands, or very low polarizabilities of some of the modes or masking of the weak bands by intense bands. The band at 639 cm^?1 is tentatively assigned to the TiO symmetric stretching vibration (γ₁) and the bands at 495 and 471 cm^?1 to torsional modes. The bands in the region 180–340 cm^?1 are assigned to the OTiO bending modes and the 155 cm^?1 band to the Ca(TiO₃) lattice mode. The observed Raman bands are compared with the available infrared absorption data and, as expected, some coincidences in frequencies are seen for this compound with a noncentrosymmetric structure.     

Formate anion: The physical force field

Unequivocal assignments for all of the vibrational modes of the formate ion have been made from isotopic shifts measured in the Fourier transform infrared and Raman spectra of polycrystalline samples of the sodium salts of HCO₂^?, H¹³CO₂^?, DCO₂^?, and D¹³CO₂^?. Literature frequencies for DCO¹⁸O^? and DC¹⁸O₂^? have been added to the above results for the unique determination of the 10 force constants in the general harmonic force field. Product rule relations among the harmonic frequencies are shown to interfere seriously with the determination of the physical force field by the standard normal coordinate computation. The least-squares refinement is found to be particularly sensitive to identified types of anharmonic error in the frequencies. Refinements characterized as Φ^aH and Φ^aD improve reliability by elimination of the deuterium isotopic shift for νCH. The physical force field is interpreted in terms of the geometric and electronic structure.     

High frequency waves in liquid metals

The inelastic scattering of long wavelength neutrons from coherently scattering metals has been used to examine the collective motions of atoms in the liquid state and to make comparisons with the polycrystalline solids. Well-defined peaks in the velocity spectra of the scattered neutrons have been found in both states for lead, rubidium, tin, bismuth and aluminium. These have been used to present parts of the dispersion curves for vibrational modes of motion in the frequency range 1 to 20 × 10¹² rad/sec and wave number range 1 to 3 Å^?1, and to estimate lifetimes of the modes of the order 0.4 × 10^?12 sec in the solid near the melting point and roughly half these values in the liquid.

In polycrystalline aluminium the major contribution to the observed intensity in the solid is due to transverse modes and the observed similarity of the liquid and solid spectra suggests that transverse motions are observed in the liquid also.     

Defect modes due to H− - D− pair impurities in KCl and KBr

Localised modes due to H^? - D^? pair impurities aligned in the [110] direction in KCl and KBr have been computed using a Green's function approach. The defect space used consists of 12 particles; the two defect ions (H^? and D^?) and their ten nearest neighbours (K⁺ ions). The system has C_2ν site symmetry around the defect ions, and this property has been used to block diagonalise the relevant 36 × 36 matrix by group theoretical techniques. Various irreducible representations thus obtained have been used to compute the defect modes. Numerical values of the various Green's functions computed on the basis of neutron-fitted shell model parameters were used. Mass changes as well as changes in the short range interactions were considered while forming the perturbation matrix. The localised modes computed are seen to be in good agreement with the experimentally observed values.     

Drift study of the products formed by radiolysis and photolysis of alkaline nitrates

The products of the radiolysis and photolysis of crystalline sodium, potassium, rubidium, cesium nitrates have been investigated by the diffuse reflectance infrared Fourier transform spectroscopy. The bands in the 1260-1220 and 804-809 cm^?1 regions observed after the n -irradiation and photolysis by a light with the wave length 253.7 nm of crystalline alkali nitrates were identified as the vibrational modes of NO^? ₂ x ₃ and x ₂, respectively. The frequency of the x ₃ oscillation of nitrite ions decreases from 1260 cm^?1 up to 1220 cm^?1 with the increase of the atomic weight or polarizability of a cation. The detection limit of the nitrite ions (1 ‐ 10^?7 mol g^?1) for the diffuse reflection method has been determined. The bands observed in KNO₃, RbNO₃ and CsNO₃ spectra in the 947-940 and 722-737 cm^?1 regions appearing only after photolysis are due to stretch oscillations of the peroxide bond O-O and wagging oscillations of the -ON=O group of peroxynitrite accordingly.     

Vibrational Spectroscopic Studies of Molecules with Biochemical Interest: The Cysteine Zwitterion

Abstract

The L-cysteine zwitterions in the orthorhombic crystal structure and in aqueous solution, including the deuterated isotopologues HSCD₂CH(NH₃ ⁺)COO^?, DSCH₂CH(ND₃ ⁺)COO^?, and DSCD₂CH(ND₃ ⁺)COO^?, have been studied by mid-infrared, far-infrared, and Raman spectroscopy. Density functional theory (DFT) calculations were performed for an equilibrium molecular geometry of the cysteine zwitterion to obtain vibrational frequencies of fundamental modes, infrared (IR) and Raman intensities, and the depolarization ratio of the Raman bands and combined with normal coordinate force field analyses. The force field obtained for dissolved (in H₂O and D₂O) cysteine, based on the 4 × 36 experimental fundamental modes of the four isotopologues, was successfully transferred to the two conformers in the solid state. The experimentally observed multiple bands (generally doublets) of L-cysteine and its deuterated isotopologues in the solid state were interpreted based on the coexistence of two conformers in the unit cell. The calculated frequencies were used for full assignments of the fundamental IR and Raman vibrational transitions, including an attempt to interpret all low-frequency vibrations (below 400 cm^?1) of the zwitterion also in the solid state. In particular, the hydrogen bonding effects on conformation, bond lengths, and force constants were studied, including those of the distorted NH₃ ⁺ amino group. The –S-H and -S-D stretching vibrations were found to be local modes, not sensitive to deuterium substitution of the -CH₂ and -NH₃ ⁺ groups in the molecule or to the H(D)-S-C-C torsional angle. The two major -S-H or -S-D stretching bands observed in the solid state correspond to different S-H/D bond lengths and resulted in the force constants K _SH = 3.618 N·cm^?1 and 3.657 N·cm^?1 for the SH^… S and SH^… O hydrogen-bonded interactions. A remarkable result was that the S(H)^… O interaction was weaker than the S(H)^… S interaction in the solid state and even weaker in aqueous solution, K _SH = 3.715 N·cm^?1, possibly due to intramolecular interactions between the thiol and amino groups. A general correlation between the S-H/D bond length and vibrational frequency was developed, allowing the bond length to be estimated for sulfhydryl groups in, for example, proteins. The C-S stretching modes were fitted with different C-S stretching force constants, K _CS = 3.213 and 2.713 N·cm^?1, consistent with the different CS bond lengths for the two solid-state conformers.     

Infrared absorption of aligned H−Na+H− complexes in Kcl crystals

The localized vibrations of a complex in KCl consisting of a triangular array of two H^? ions and one Na⁺ ion in substitutional, neighboring positions have been observed in infrared absorption. As one would expect for such a molecule, five modes are observed: two longitudinal modes at 365 and 508 cm^-1, two complanar transverse modes along <110> at 459 and 562 cm^?1, and one transverse mode along <100> at 551 cm^?1.     

Enhancement in electrochemical properties of ionic liquid-based nanocomposite polymer electrolytes by 100 MeV Si9+ swift heavy ion irradiation

Swift heavy ion (SHI) irradiation has been used as a tool to enhance the electrochemical properties of ionic liquid-based nanocomposite polymer electrolytes dispersed with dedoped polyaniline (PAni) nanorods; 100 MeV Si⁹⁺ ions with four different fluences of 5?×?10¹⁰, 1?×?10¹¹, 5?×?10¹¹, and 1?×?10¹² ions cm^?2 have been used as SHI. XRD results depict that with increasing ion fluence, crystallinity decreases due to chain scission up to fluence of 5?×?10¹¹ ions cm^?2, and at higher fluence, crystallinity increases due to cross-linking of polymer chains. Ionic conductivity, electrochemical stability, and dielectric properties are enhanced with increasing ion fluence attaining maximum value at the fluence of 5?×?10¹¹ ions cm^?2 and subsequently decrease. Optimum ionic conductivity of 1.5?×?10^?2 S cm^?1 and electrochemical stability up to 6.3 V have been obtained at the fluence of 5?×?10¹¹ ions cm^?2. Ac conductivity studies show that ion conduction takes place through hopping of ions from one coordination site to the other. On SHI irradiation, amorphicity of the polymer matrix increases resulting in increased segmental motion which facilitates ion hopping leading to an increase in ionic conductivity. Thermogravimetric analysis (TGA) measurements show that SHI-irradiated nanocomposite polymer electrolytes are thermally stable up to 240–260 °C.     

Localised vibrations due to substitutional impurities in calcium fluoride

The localized modes in CaF₂ due to the introduction of substitutional impurities have been investigated using the greens functions method. The weakening of the nearest neighbour interaction in all the alkaline earth fluorides, is estimated from the infrared absorption spectra on localized modes in these crystals. The splitting of the localized modes in CaF₂, due to the presence of additional Sr²⁺ or Ba²⁺ impurities is estimated and satisfactory agreement exists between theory and experiment, within the limits of the simplifications in our calculations.     

Far infrared optical properties of NbSe3

We have measured the far infrared reflectance of NbSe₃ and used models of the frequency dependent conductivity to fit the data. General arguments show that at 2 K a charge density wave (CDW) energy gap exists between 120 and 190 cm^?1, the relaxation time(s) of the free carriers and CDW pinned mode is >30×10^?12 s, and the ratio of the free carrier concentration to band mass is <2×10²⁰ cm^?3/m₀.     

Raman scattering from 6Li+ and 7Li+ ions in lithium beta-alumina

Raman bands due to translational modes of ⁶Li⁺ and ⁷Li⁺ ions in beta-alumina were found in the frequency range of 340–410 cm^?1, which is much higher than expected from the corresponding values reported for other alkali-metal ions (20–100 cm^?1). Based on a model calculation, it is believed that the large shifts to higher frequencies are due to deviations of the Li⁺ ions from the mirror plane into “pocket sites” formed by oxygen ions above or below the Beevers-Ross sites     

Far-infrared reflectivity of KI:Cl? and KI:Na+

The far-infrared reflectivity spectra of KI doped with 1% Cl^– and 2% Na⁺ were measured using a dual cavity technique. In addition to the observation of all previously-observed resonant and gap modes, several features were discovered in and near the optic band. A new gap mode at 90 cm^–1 in KI:Cl^– was discovered. In both systems sharp, narrow reductions in reflectivity at 98, 108, 116, and 139 cm^–1 were observed, as was a general reduction in reflectivity between 108 and 139 cm^–1. The structure at 98 and 116 cm^–1 is most-likely due to optical activity induced in normally inactive lattice modes by the high concentration of impurities. The features at 108 and 139 cm^–1 and the reduction in reflectivity between them were shown by a simple model calculation to be due to an increase in damping of the TO phonon.