Collision-induced absorption (CIA) spectra and ground-state potentials of inert gas mixtures

Collision-induced absorption spectra of the rare gas systems He-Ne, He-Ar, He-Kr, He-Xe, Ne-Kr, Ne-Xe, Ar-Kr and Ar-Xe at different temperatures with the pressure second virial coefficients, viscosity and thermal conductivity have been used for deriving the empirical models of the induced dipole moment and the interaction potential. Theoretical zeroth, first and second moments of the binary spectra using various models for the induced dipole moment and interatomic potential are compared with the experimental values performed by the groups of Marteau, Bosomworth, Bucktoyarova, Bar-Ziv, Ryzhov and Frommhold. In addition, mixture diffusion coefficients and isotopic thermal factors calculated for these models are compared with experimental ones. The results show that these models are the most accurate models reported to date for these mixtures.     

Phenomenological model and experimental study of DNA absorption spectra in THz range

The dielectric permittivity tensor is analyzed qualitatively for the DNA nematic liquid crystal in the THz frequency range. The analysis is performed within the self-consistent phonon approximation based on the PBD model. It is found that DNA depolarization and absorption spectra depend on such parameters as molecular length and helix period. Specifically it is shown that a localization of the absorption lines in the frequency range is determined by the DNA helix structure whereas the DNA length is responsible for a separation between the absorption lines. It is also shown that the gyrotropic properties of the considered liquid crystal depend on a relation between the molecular length and its helix period. The molecules with even number of half helix periods demonstrate the strongest gyrotrophy whereas the molecules with odd number of half helix periods have the weakest gyrotrophy. The model is used to suggest the experimental methodology for determining the DNA length and helix structure based on measurements of the depolarization and absorption spectra in aqueous solutions of biopolimers. Methods of applied THz spectroscopy for determination of the conformational state of molecules in solution is announced. Some preliminary experimental results are presented, including details of measuring the absorption spectra of dry DNA sample and aqueous solutions of biopolimers.     

Far infrared spectra of the D2 and the D2-He systems

The rototranslational absorption spectra of D₂ and D₂ - He at 92K have been measured at different densities and different D₂ concentrations. From these spectra we have derived the translational line-shape; the observed density effects and, in particular, the relevance of the two-body and the three-body contributions have been discussed by comparing the line-shape derived from the D₂ spectra with the two-body term obtained from the analysis of the D₂ - He spectra.     

Qualitative and quantitative differences in the absorption spectra of electron-irradiated reflective coatings based on mixtures of BaTio3 powder with ZrO2 micro- or nanopowder of different concentrations

The effect of the concentration and size (micro- or nanoparticles) of zirconium dioxide powders, heated in mixtures with barium titanate powder, on the radiation resistance of reflecting coatings on their basis is analyzed during accelerated electron irradiation. It is shown that nanoparticles provide increased radiation resistance of the coatings compared to microparticles.     

First-principles study on the electronic structures and absorption spectra for the PbWO4 crystal with lead vacancy

The electronic structures and absorption spectra for the perfect PbWO₄ (PWO) crystal and the crystal containing lead vacancy have been calculated using density functional theory code CASTEP with the lattice structure optimized. The calculated absorption spectra of the PWO crystal containing exhibit seven absorption bands peaking at 1.72 eV (720 nm), 2.16 eV (570 nm), 2.81 eV (440 nm), 3.01 eV (410 nm), 3.36 eV (365 nm), 3.70 eV (335 nm) and 4.0 eV (310 nm), which are very close to the experimental values. It predicts that the 330, 360, 420, 500-750 nm absorption bands are related to the existence of in the PWO crystal.     

Far infrared laser magnetic resonance spectra of the ClSO and FSO radicals in the gas phase

The detection of the free radicals ClSO and FSO by the technique of far infrared laser magnetic resonance is reported. Observations of the former have been made with several laser lines; the spectra are complicated and have not been assigned but are attributed to ClSO on the basis of several chemical tests. The FSO radical was generated by the reaction of carbon disulphide with the products of a discharge through CF₄ + O₂. Spectra have been observed with laser lines at 394, 419 and 513 μm. Using the results of a subsequent microwave study of FSO, the rotational transitions involved in these spectra have been identified. The spectrum at 513 μm has been studied in detail and is shown to arise through level anticrossings between the levels 14_5,Kc (the lower levels involved in the transition) and 15_4,Kc+2. All aspects of this spectrum are reproduced quantitatively by the parameters determined from the microwave spectrum. It is thought that the other two FSO spectra arise in a similar manner. Such anticrossing signals are likely to be widespread in LMR experiments, causing intense narrow lines to occur at high magnetic fields even for molecules with weakly coupled electron spin.     

Far infrared absorption in ultrafine metallic particles: Calculations based on classical and quantum mechanical theories

Detailed calculations of far infrared absorption in ultrafine metallic particles are reported. Effective medium treatments of the composite of particles and their surrounding are carried out within the Maxwell Garnett and Bruggeman theories. Generalizations of these to encompass dipole-dipole interaction and oxide pellicles are discussed. The dielectric permeability of the particles is specified either by the Drude (D) model with a size limited mean free path, or by the quantum mechanical derivation of Gor'kov and Éliashberg (GE). Excepting narrow diameter (x) and frequency ( ) intervals the absorption coefficients can be approximated by =fCx , wheref is the filling factor (taken to be small),C is a constant which depends on the free electron parameters, and and are integers. Results for largerfs are included also. The magnitudes ofC, and differ in general for the Drude and Gor'kov-Éliashberg theories; they are also different forxx ^C , wherex _D ^C 5 nm andx _GE ^C is typically 20 nm. The quantityx ^c signifies a transition from a range where is dominated by the dielectric polarisation to one where the magnetic polarisation is largest. An interesting multiple peak structure is found from detailed calculations of _GE vs. for sufficiently small identical particles. Effects of log-normal size distributions are derived explicitely; any fine structure in the _GE vs.x functions is found to be completely washed out for practically attainable distribution widths.Work at Cornell University was supported by the National Science Foundation through the Materials Science CenterWork at Chalmers University of Technology was supported by the Swedish Natural Science Research Council     

Inhibition of the reduction of Cr(VI) at the magnetite–water interface by calcium carbonate coatings

The effect of calcium carbonate coatings on the reduction of aqueous chromate on the magnetite(1 1 1) surface has been investigated using a combination of synchrotron based X-ray photoemission spectroscopy (PES) and X-ray absorption near edge structure (XANES) spectroscopy, along with laboratory-based powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). CaCO₃ coatings (dominantly calcite with minor quantities of aragonite and vaterite) of thicknesses ranging from 10 Å to 20 m were grown on magnetite(1 1 1) surfaces by exposure to supersaturated aqueous solutions followed by evaporation of the solution—a process that mimics pore-water evaporation in vadose zones leading to the formation of caliche and calcium carbonate coatings on mineral grains. Coating thicknesses were determined from attenuation of the Fe 2p photoemission signal by the carbonate coating. For coatings less than 15 Å thick, Cr 2p photoemission and Cr L_II, L_III-edge XANES spectra show that chromate is reduced by the underlying magnetite surface; however, as the minimum coating thickness increases beyond 15 Å, the magnetite surface becomes passivated and further chromate reduction ceases. Our findings suggest that carbonate coatings on natural magnetite grains can significantly reduce or eliminate their ability to reduce Cr(VI), which is a toxic and highly mobile environmental contaminant.     

Polarized absorption spectra and spectroscopic parameters of Tm3+ in the TmAl3(BO3)4 single crystal

High-optical-quality single crystals of the TmAl₃(BO₃)₄ compound were synthesized from a solution in the melt. The absorption spectra in the σ and π polarizations for the ³ H ₆ → ³ F ₄, ³ H ₆ → ³ H ₅, ³ H ₆ → ³ H ₄, ³ H ₆ → ³ F ₃, ³ H ₆ → ³ F ₂, ³ H ₆ → ¹ G ₄, and ³ H ₆ → ¹ D ₂ transitions in the Tm³⁺ ion were recorded at room temperature. The transition intensities were analyzed in the framework of the Judd-Ofelt theory generalized to the case of anisotropic crystals, and the following parameters of the theory were obtained: Ω₂ = 6.14 × 10^?20 cm², Ω₄ = 3.09 × 10^?20 cm², and Ω₆ = 2.04 × 10^?20 cm². The lifetimes and the branching ratios were determined for all possible transitions.     

Infrared absorption spectra of a Nd0.5Ho0.5Fe3(BO3)4 crystal

Infrared absorption spectra of a Nd_0.5Ho_0.5Fe₃(BO₃)₄ crystal in the spectral range of 30–1700 cm^–1 have been measured at temperatures from 6 to 300 K. The experimental spectra have been analyzed based on the semiempirical calculation of the lattice dynamics and the analysis of correlation diagrams of borate complexes. No changes associated with structural phase transitions have been detected in the temperature range of measurements; the effect of magnetic ordering on the infrared absorption spectra has not been observed.     

Optical spectra of calcium atoms in inert matrices: A new red absorption for Ca2

Calcium atoms codeposited with N₂, Ar, Kr, and Xe on a sapphire plate at 10, 17, or 29 K exhibited very strong, sharp absorptions due to the resonance transition of isolated Ca atoms and broad bands in the green region which show Ca concentration dependence characteristic of aggregated species. A red absorption contained sharp vibronic fine structure with 117 cm^?1 spacings in solid krypton which decreased to 111 cm^?1 with ⁴⁴Ca deposition. The structured absorption is assigned to the $\text{A}{}^1\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}\text{(}{}^1\text{S +}{}^1\text{P) ← X}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}\text{(}{}^1\text{S +}{}^1\text{S)}$ transition of Ca₂.     

Decoupling multimode vibrational relaxations in multi-component gas mixtures: Analysis of sound relaxational absorption spectra

Decoupling the complicated vibrational-vibrational (V-V) coupling of a multimode vibrational relaxation remains a challenge for analyzing the sound relaxational absorption in multi-component gas mixtures. In our previous work [Acta Phys. Sin. 61 174301 (2012)], an analytical model to predict the sound absorption from vibrational relaxation in a gas medium is proposed. In this paper, we develop the model to decouple the V-V coupled energy to each vibrational- translational deexcitation path, and analyze how the multimode relaxations form the peaks of sound absorption spectra in gas mixtures. We prove that a multimode relaxation is the sum of its decoupled single-relaxation processes, and only the decoupled process with a significant isochoric-molar-heat can be observed as an absorption peak. The decoupling model clarifies the essential processes behind the peaks in spectra arising from the multimode relaxations in multi-component gas mixtures. The simulation validates the proposed decoupling model.