Theoretical investigations of the SH and LiS cations

Reliable theoretical data on spectroscopy and spin-orbit matrix elements are computed for the lowest electronic states of SH⁺ and LiS⁺ ions. Accurate spectroscopic predictions for their excited electronic states are given. For SH⁺, polarization minima at large internuclear distances are located in addition to the strongly bound electronic states already known. For LiS⁺, our calculations confirm that the electronic ground state of this ion is of ³Σ⁻ species and reveal the existence of a ¹Δ state presenting a potential well as deep as the potential of the ground state. Moreover, the LiS⁺ electronic excited states potential energy curves possess shallow potential minima in the molecular region and at long-internuclear distances. Generally, these shallow minima may be populated during low energy collisions between the corresponding atomic fragments. Finally, spin-orbit calculations have allowed giving accurate determinations of the spin-orbit splittings for these cations and elucidation of the predissociation mechanisms of SH⁺ leading to the formation of the S⁺ and H species in their electronic ground states. Accordingly, long-lived SH⁺ ions can be found in the X³Σ⁻, a¹Δ and b¹Σ⁺ electronic states and the rovibrational levels of LiS⁺ in its electronically excited and ground states should be weakly perturbed.     

The rotational spectrum of the SH radical in its XΣ state

All the available data on the rotational energy levels of the SH⁺ (sulfoniumylidene) radical in the v = 0 and 1 levels of the X³Σ⁻ ground state have been subjected to a single, weighted least-squares fit to determine an improved set of molecular parameters for this molecule. The results have been used to calculate the rotational spectrum of the SH⁺ radical in the v = 0 and 1 levels up to the N = 4-3 transition.     

Calculations of the Overtone Transitions Of Sh− Pairs In KCl

In this work all vibration transitions up to the second overtone of pair SH^? molecules in KCl were calculated. The interaction of the identical molecules, which are characterized by “exact” resonance (equal pairs “SH^?—”SH^?, n = 32,33,34,36) were researched. The unequal molecular ions—“inexact” interaction (unequal pairs, “SH^?—^kSH^?, n≠ k, n, k = 32,33,34,36) were also considered. In both cases the problem was to find the eigenvalues of the matrix of dipole—dipole interaction that conforms to the solution of a secular equation. The elements of the dipole—dipole matrix were calculated in terms of the mechanical anharmonicity. It was supposed that the function of the dipole moment has linear dependence on the vibrational coordinate. The conditions of “exact” resonance and the conditions of “inexact” resonance diverged considerably. In the case of the “exact” resonance we used the orthogonal transformation of the dipole-dipole matrix and obtained a precise solution. In case of the “inexact” resonance we used the method of successive diagonalization. The intensities of the pair lines were calculated as well.     

Chemomechanical properties and microstructural stability of nanocrystalline Pr-doped ceria: An in situ X-ray diffraction investigation

The chemomechanical properties and microstructural stability of nanocrystalline Pr_xCe_1 − xO_2 − δ solid solutions are studied as a function of temperature by in situ X-ray diffraction measurements under oxidizing conditions at P(O₂) ~ 200 mbar. The chemical expansion coefficient of nanocrystalline powder specimens, operative at intermediate temperatures during which Pr⁴⁺ is reduced to Pr³⁺, is found to be similar to that obtained for coarse-grained Pr_xCe_1 − xO_2 − δ. This is contrary to reports regarding variation of physical and chemical properties with crystallite size. The thermal expansion coefficient, measured under conditions for which Pr_xCe_1 − xO_2 − δ is highly oxygen deficient, was found to be greater than that measured for fully oxidized Pr_xCe_1 − xO_2 − δ, with potential sources of these changes discussed. Moreover, the microstructure of nanocrystalline Pr_xCe_1 − xO_2 − δ is observed to have excellent stability at working temperatures below 800 °C, enabled by the inherent microstrain in the structure, highlighting the potential application of this material for solid state electrochemical devices.     

ESR and optical study of Mn doped potassium hydrogen sulphate

The ESR spectrum of Mn²⁺ doped potassium hydrogen sulphate at liquid nitrogen temperature (77 K) has been analyzed and site of entered Mn²⁺ in the lattice has been discussed. The values of the zero field parameters that give good fit to the observed ESR spectra have been obtained. The obtained g, A, B, D, E and a values are 2.0002, 66×10⁻⁴ cm⁻¹, 26×10⁻⁴ cm⁻¹, 59×10⁻⁴ cm⁻¹, 32×10⁻⁴ cm⁻¹ and −8×10⁻⁴ cm⁻¹, respectively. The percentage of covalency of the metal-ligand bond has also been estimated. From the optical absorption study at room temperature, the distortion has been suggested. The observed bands are assigned as transitions from the ⁶A_1g(S) ground state to various excited quartet levels of Mn²⁺ ion in a cubic crystalline field. The electron repulsion and crystal field parameters B, C, Dq and α providing good fit to the observed optical spectra have been evaluated and the values obtained for the parameters are B=627 cm⁻¹, C=2580 cm⁻¹ , Dq=790 cm⁻¹ and α=76 cm⁻¹.     

FTIR stretching-mode measurements and calculations of equal and unequal pairs of SH− and SD− defects in KCI

Abstract

The fundamental stretching-mode absorption of molecular defects (ⁿSH^? or ⁿSD^?, where n = 32, 33, 34, 36) in KCI has four clear isotope-split lines. Due to the resonance interaction of the defects in pairs the absorption band of pair defects does not show the same isotope structure. We present here a theoretical approach for studying this phenomenon in KCI:SH:SD. The ions are assumed to preserve the [111] orientation of isolated defects and occupy the nearest neighbour anion sites. The results of the calculation show that the SH^? ions in the pair should have parallel or antiparallel directions to agree with the experimental spectrum.     

Elemental depth profiling of a-Si1−xGex:H films by elastic recoil detection analysis and secondary ion mass spectrometry

The hydrogen content in a-Si_1−xGe_x:H thin films is an important factor deciding the density and the optical band gap. We measured the elemental depth profiles of hydrogen together with Si and Ge by elastic recoil detection analysis (ERDA) combined with Rutherford backscattering (RBS) using MeV He²⁺ ions. In order to determine the hydrogen depth profiles precisely, the energy- and angle-dependent recoil cross-sections were measured in advance for the standard sample of a CH₃⁺-implanted Si substrate. The cross-sections obtained here are reproduced well by a simple expression based on the partial wave analysis assuming a square well potential (width: r₀ = 2.67 × 10⁻¹³ cm, depth: V₀ = −36.9 MeV) within 1%. For the a-Si_1−xGe_x:H films whose elemental compositions were determined by ERDA/RBS, we measured the secondary ions yields of HCs₂⁺, SiCs₂⁺, H⁻, Si⁻ and Ge⁻ as a function of Ge concentration x. As a result, it is found that the useful yield ratios of HCs₂⁺/SiCs₂⁺, H⁻/Si⁻ and Ge⁻/Si⁻ are almost constant and thus the elemental depth profiles of the a-Si_1−xGe_x:H films can be also determined by secondary ion mass spectrometry (SIMS) within 10% free from a matrix effect.     

Effects of Cl, NO3 and SO4 anions on the anodic behavior of carbon steel in deaerated 0.50 M NaHCO3 solutions

The effects of Cl⁻, NO₃⁻ and SO₄²⁻ aggressive anions on the corrosion and passivation behavior of carbon steel electrode in deaerated 0.50 M NaHCO₃ solutions were studied using potentiodynamic anodic polarization and SEM techniques. It was found that the presence of Cl⁻, NO₃⁻ and SO₄²⁻ anions stimulates the anodic dissolution rate in both the active and the pre-passive potential regions. Moreover, significantly great effects were observed in both the passive and the trans-passive potential regions. Pitting corrosion was observed only in the presence of Cl⁻ anions, while the presence of NO₃⁻ and SO₄²⁻ anions facilitate only passivation by oxygen of water without themselves participating in the cathodic process. Also, it was observed that the effect of NO₃⁻ anion, which is a strong oxidizing agent acting “primarily” as stimulator of the cathodic process and then its reaction product acts “indirectly” retarding the anodic process. On the other hand, the effect of SO₄²⁻ anion, which is a non-oxidizing agent, exerts an “indirect” effect on the cathodic reaction increasing its rate and then “directly” influence on the anodic reaction, retarding it.     

Laser-induced swelling of transparent glasses

We describe the process of forming bumps on the surface of transparent glasses such as display glasses with moderate thermal expansion ∼3.2 × 10⁻⁶ K⁻¹ and high coefficient of thermal expansion (CTE) glasses, e.g. soda-lime glasses with CTE ∼9 × 10⁻⁶ K⁻¹ using high-power ultra-violet (UV) lasers at a wavelength where glass is transparent. We characterize the effect with optical dynamic measurements. The process relies on increased glass absorption from color-center generation and leads to glass swelling with bumps formation. The bump height may constitute more than 10% of the thickness of the glass sample. The required exposure time is relatively short ∼1 s, and depends on the glass properties, laser power, its repetition rate, and focusing conditions. A brief review of the potential applications for these bumps is provided.     

χ measurement and optical limiting studies of urea picrate

The molecular charge complex urea picrate (UP) was synthesized and its third order nonlinear optical properties have been investigated using a single beam Z-scan technique with nanosecond laser pulses at 532 nm. Open aperture data of the compound indicates two photon absorption at this wavelength. The nonlinear refractive index n₂, nonlinear absorption coefficient β, magnitude of effective third order susceptibility χ⁽³⁾, the second order hyperpolarizability γ_h and the coupling factor ρ have been estimated. The experimentally determined values of β, n₂, Re χ⁽³⁾ and Im χ⁽³⁾, γ_h and ρ of the compound UP are 2.146 cm/GW, −1.258×10⁻¹¹ esu, −1.347×10⁻¹³ esu, 0.377×10⁻¹³ esu, 0.69×10⁻³² esu and 0.28, respectively. The compound exhibits good optical limiting at 532 nm with the limiting threshold of 80 μJ/pulse. Our studies suggest that compound UP is a potential candidate for optical device applications such as optical limiters.     

Electrochemiluminescence of fluorescein in alkaline solution at a polycrystalline gold electrode

The electrochemiluminescence (ECL) behavior of fluorescein at a polycrystalline gold electrode was studied under conventional cyclic voltammetric conditions. Five ECL peaks were observed at 0.94 (ECL-1), 1.51 (ECL-2), 1.34 (ECL-3), −0.06 (ECL-4), −0.73 to −1.11 V (ECL-5, a broad weak wave) (vs. SCE), respectively, on the curve of ECL intensity versus potential. These ECL peaks were found to depend on the pH of the solution, supporting electrolyte, potential scan ranges and directions. The emitter of ECL peaks was identified as fluorescein or eosin Y produced on the electrode by analyzing the ECL spectra and fluorescence spectra. The mechanisms for ECL peaks have been proposed due to the reactions of fluorescein and the electro-oxidation product of fluorescein with various oxygen-containing species in the solution or electrogenerated at different applied potentials such as O₂, O₂^·−, HO₂⁻, and BrO⁻. Singlet molecular oxygen was generated during the reactions and transferred its energy to the ECL emitter such as fluorescein or eosin Y, emitting light.     

The Hot Bands of Methane between 5 and 10 μm

Experimental line intensities of 1727 transitions arising from nine hot bands in the pentad–dyad system of methane are fitted to first and second order using the effective dipole moment expansion in the polyad scheme. The observed bands are ν₃− ν₂, ν₃− ν₄, ν₁− ν₂, ν₁− ν₄, 2ν₄− ν₄, ν₂+ ν₄− ν₂, ν₂+ ν₄− ν₄, 2ν₂− ν₂, and 2ν₂− ν₄, and the intensities are obtained from long-path spectra recorded with the Fourier transform spectrometer located at Kitt Peak National Observatory. For the second order model, some of the 27 intensity parameters are not linearly independent, and so two methods (extrapolation and effective parameters) are proposed to model the intensities of the hot bands. In order to obtain stable values for three of these parameters, 1206 dyad (ν₄, ν₂) intensities are refitted simultaneously with the hot band lines. The simultaneous fits to first and second order lead to rms values respectively of 21.5% and 5.0% for the 1727 hot band lines and 6.5% and 3.0% for the 1206 dyad lines. The band intensities of all 10 pentad–dyad hot bands are predicted in units of cm⁻²atm⁻¹at 296 K to range from 0.931 (for 2ν₄− ν₄) to 7.67 × 10⁻⁵(for 2ν₄− ν₂). The total intensities are also estimated to first order for two other hot band systems (octad–pentad and tetradecad–octad) that give rise to weak transitions between 5 and 10 μm.     

Fluorophosphate glasses containing manganese

New fluorophosphate glasses based on MnF₂, NaPO₃ and MF_n (M=Zn²⁺, Sr²⁺, Mg²⁺, Ba²⁺, Li⁺, Na⁺ and K⁺) have been synthesised and characterized. Large vitreous areas were observed. Samples of 4 mm in thickness have been obtained. These glasses are easy to prepare and stable in ambient air. Depending on the composition and the nature of the M cation, glass transition temperature, T_g, lies between 230 and 314 °C, crystallisation temperature, T_x is between 320 and 475 °C. These glasses are pink coloured, and infrared transmission extends up to 4.5 μm with extrinsic OH⁻ absorption band at 3200 cm⁻¹ and other bands around 2200 and 1600 cm⁻¹ that relate to PO₄ tetrahedron vibration. Other physical properties including density, microhardness, Young modulus, thermal expansion and refractive index were investigated and correlated to composition.     

pH dependence of electrokinetic behavior of dolomite and magnesite in aqueous electrolyte solutions

In this paper, electrokinetic potential and isoelectric point of dolomite (CaMg(CO₃)₂) and magnesite (MgCO₃) were determined. The effect of various ions such as Mg²⁺, Ca²⁺, Na⁺ and CO₃²⁻ on surface properties of dolomite and magnesite were also examined. Isoelectric points of dolomite and magnesite were determined as 6.3 and 6.8, respectively, in the absence of any electrolyte. H⁺ and OH⁻ ions are the potential determining ions of magnesite and dolomite, as predicted by electrokinetic potential studies.     

Microwave spectrum of 2-aminopyridine

The microwave spectra of 2-aminopyridine-NH₂, -ND₂, and of both of the two possible -NHD molecules have been observed and assigned in the 0⁺ vibrational state of the amino group inversion vibration; the assignment for three of the molecules in the 0⁻ state is also made. From intensity measurements the 0⁺-0⁻ splitting is estimated to be 135 ± 25 cm⁻¹ for the -NH₂ molecule and 95 ± 30 cm⁻¹ for the -ND₂ molecule. The rotational constants are interpreted in terms of a structure in which the amino group is bent about 32° out of the molecular plane, the c coordinates of the two amino H atoms being 0.21 and 0.28 Å. Stark effect measurements give a dipole moment of about 0.9 D which is almost entirely in the b axis, and which changes quite significantly between the 0⁺ and 0⁻ states.     

Curcumin as a colorimetric and fluorescent chemosensor for selective recognition of fluoride ion

The binding properties of curcumin with anions in acetonitrile were examined for the first time by UV-vis absorption and fluorescence spectroscopies. The results showed that curcumin highly and selectively responded to F⁻ over other anions such as AcO⁻, H₂PO₄⁻ and Cl⁻ because of anionic complex formation via hydrogen bond. Curcumin gave rise to the red-shift of absorption spectra and its fluorescence was quenched with concomitant color change from yellow to purple upon addition of F⁻, which was detected by naked eyes. The addition of other anions such as AcO⁻, H₂PO₄⁻, HSO₄⁻, NO₃⁻, Cl⁻ and Br⁻ did not result in observable spectral change and solution color change. The binding constant between curcumin and F⁻ was 2.0×10⁵ mol⁻¹ L and the recognizing mechanism was investigated as well.     

Experimental determination of pressure-broadening parameters of millimeter-wave transitions of HNO3 perturbed by N2 and O2, and of their temperature dependences

We report on linewidth measurements on the J=24_K,11−23_K^′,10 and J=38_K,33−37_K^′,32 millimeter wave transitions in the ground vibrational state of nitric acid, located near 470.23 and 544.36 GHz, respectively. Experiments were performed with N₂ and O₂ as perturber molecules, in the 240-350 K temperature range by using a video-type spectrometer. The foreign-gas broadening parameters and their temperature dependence coefficients were determined using the Voigt profile, no narrowing effect being observed. In order to check the reliability of reported values, we carried out measurements on the J=14_K,12−13_K^′,11 transition located near 206.6 GHz, previously observed in two other laboratories. For this last line all the reported values are consistent themselves within one claimed standard deviation.     

Microgravimetric and voltammetric study of Zn underpotential deposition on platinum in alkaline medium

The microgravimetric and voltammetric responses of a polycrystalline Pt electrode in 0.1 mol L⁻¹ NaOH solution in the presence and the absence of 1.6 × 10⁻⁴ Zn²⁺, at 0.1 V s⁻¹ were analyzed. During the positive potential sweep, the water molecules are progressively substituted by OH⁻ ions, prior to PtO formation. The voltammetric charges obtained under the Zn_ads dissolution peaks suggest that 0.7 monolayers are deposited, with each Zn ad-atom occupying one active site and transferring two electrons. The total loss of mass due to the dissolution of the Zn ad-layer was 136.6 ng cm⁻² and the mass increase due to PtO formation was found to be only 12 ng cm⁻² less than the theoretical ones, 157.5 and 37.4 ng cm⁻², respectively, indicating that both processes are overlapped. In this way it is proposed that an adsorbed by-layer of Zn and OH⁻ ions is formed.     

Electrical transport properties of CaMnO3 thermoelectric compound: a theoretical study

The electrical transport coefficients of anti-ferromagnetic CaMnO₃ have been investigated by density functional theory calculation within generalized gradient approximation. The calculated transport coefficients exhibit the anisotropic nature, in agreement with its electronic states. The transport property results reveal the stronger carrier transport along the O1–Mn–O1 plane within the O–Mn–O octahedron, indicating that the Mnd and O1p orbitals are mainly responsible for electrical transport. The maximum power factor values as a function of relaxation time reach 8.4×10²³ Wm⁻¹ K⁻² s⁻¹, 7.9×10²³Wm⁻¹ K⁻² s⁻¹ and 4.9×10²³ Wm⁻¹ K⁻² s⁻¹ within c, a and b direction, respectively. The dimensionless figure of merit ZTxx, ZTyy as well as ZTzz is estimated with 1.28, 0.8 and 1.37 at 1000 K, respectively.     

Analysis of the high-resolution infrared spectrum of cyclopropane

The high-resolution infrared spectrum of cyclopropane (C₃H₆) has been measured from 100 cm⁻¹ to 2200 cm⁻¹. In that region we have identified 24 absorption bands attributed to six fundamental bands, five combination bands, three hot bands and 10 difference bands. Long pathlength spectra, up to 32 m, facilitated the identification and analysis of many previously unstudied infrared inactive, and Raman and infrared inactive vibrational states, including direct access to two forbidden fundamental states, ν₄ and ν₁₄. An improved set of constants for the ground vibrational state as well as for the fundamental vibrations ν₇, ν₉, ν₁₀, ν₁₁ are also reported. The spectral resolution of the measurements varied from 0.002 cm⁻¹ to 0.004 cm⁻¹.