A study of the thermal analysis of the solid solution (AgxK1−xNO3

The effect of partial replacement of K⁺ by Ag⁺ in the mixed system of KNO₃ and AgNO₃ during a set of DSC heating cycles was studied by means of a modern computerized DSC system. Thermal analysis was performed in the vicinity of the phase transition II I for pure KNO₃. The results revealed a large change in enthalpy and the phase transition temperature close to the morphotropic boundary x=0.5–0.6. At this boundary, the transformation enthalpy reached the maximum value of 101 J g^–1. On the basis of the data obtained from this accurate thermal analysis work, a model is suggested for the energy barrier of rotation of the nitrate ion in the mixed nitrate system.     

Vibrational spectrum and normal coordinate analysis of the P4S4−8 anion

The I.R. and Raman spectra of K₄P₄S₈ · 2H₂O and (NH₄)₄P₄S₈ · 2H₂O have been recorded and the vibrations of the anion have been assigned for D_4h symmetry. A normal coordinate analysis has been performed, and agreement between observed and calculated frequencies has been achieved by employing “standard” values for the PP and PS force constants, 2.05 and 2.8 [10² N m−1], respectively.     

Scaled quantum mechanical (SQM) vibrational analysis of AlCl3, Al2Cl6 and the free ion AlCl−4

A series of basis sets are evaluated for AlCl₃ and AlCl⁻₄, and a common scaling factor derived for these compounds was transferred to Al₂Cl₆. 6-31G* calculations, scaled with a common factor of 0.92, give a good fit to all vibrational frequencies for AlCl₃, AlCl⁻₄ and Al₂Cl₆, and there is also a qualitative fit between calculated and observed IR intensities. Extending the basis set does not lead to significant improvements, either for the geometry or for the vibrational frequencies. The calculations verify earlier assignments based on general valence force fields and predict frequencies for some unobserved bands. The SQM force fields for aluminium chlorides show large similarities with the isoelectronic thiophosphates; the main deviations can be attributed to more ionic bonds in the aluminium chlorides. A significant influence on the out-of-plane vibration in AlCl₃ by the basis set on the d-orbitals may indicate that π_dp bonding plays a role. A remarkable and unexpected basis set sensitivity is found for the ν₆(B_1g) ring vibration in Al₂Cl₆.     

Application of the dimer approach for the analysis of vibrational spectra of BEDT—TTF-based charge-transfer salts

The dimer approach was proposed for the normal coordinate analysis of BEDT—TTF⁺ molecular vibrations. It was shown that, within the framework of the approximation used, the appearance of additional bands in the IR as well as in Raman spectra may be explained as due to the reduction of symmetry of the dimerized system in comparison with the monomeric one. The strength of intermolecular interaction in the dimer was estimated by adjusting the calculated frequencies to the observed positions of intense “vibronic” bands recorded in the IR spectra of BEDT—TTF-based monovalent charge transfer salts. It was found that for the reproduction of “vibronic shifts” observed for some vibrations it should be assumed that the intermolecular interaction takes effect not only on the totally symmetric a_g modes, but also on the vibrations of other symmetry species.     

Normal-coordinate analysis of the TiO6−5 ion

Normal-coordinate analysis for the TiO⁶⁻₅ ion in M₂TiO₅ (M = rare earths) has been made on the basis of C_4ν-symmetry and using the Wilson's GF matrix method. The observed frequencies have been quantitatively assigned according to the obtained values of the potential-energy distributions. Force constants for the different bonds and angles have been calculated. The TiO′ (axial) and TiO (equatorial) stretching force constants were calculated to be 4.15 and 2.48 mdyn Å⁻¹, respectively.     

The vibrational spectrum and the normal coordinate analysis of β-TiCl3

The vibrational spectrum of β-TiCl₃ is reported. The observed bands are assigned on the basis of the normal coordinate analysis by use of a valence force field. It was found that the A_2u mode is lower in frequency than that in α-TiCl₃ and one of the TiTi stretchings is 281 cm⁻¹, resulting in a TiTi stretching force constant of 81.6 N/m.     

Revealing the Dominance of the Dissolution-Deposition Mechanism in Aqueous Zn−MnO2 Batteries

Zn−MnO₂ batteries have attracted extensive attention for grid-scale energy storage applications, however, the energy storage chemistry of MnO₂ in mild acidic aqueous electrolytes remains elusive and controversial. Using α-MnO₂ as a case study, we developed a methodology by coupling conventional coin batteries with customized beaker batteries to pinpoint the operating mechanism of Zn−MnO₂ batteries. This approach visually simulates the operating state of batteries in different scenarios and allows for a comprehensive study of the operating mechanism of aqueous Zn−MnO₂ batteries under mild acidic conditions. It is validated that the electrochemical performance can be modulated by controlling the addition of Mn²⁺ to the electrolyte. The method is utilized to systematically eliminate the possibility of Zn²⁺ and/or H⁺ intercalation/de-intercalation reactions, thereby confirming the dominance of the MnO₂/Mn²⁺ dissolution-deposition mechanism. By combining a series of phase and spectroscopic characterizations, the compositional, morphological and structural evolution of electrodes and electrolytes during battery cycling is probed, elucidating the intrinsic battery chemistry of MnO₂ in mild acid electrolytes. Such a methodology developed can be extended to other energy storage systems, providing a universal approach to accurately identify the reaction mechanism of aqueous aluminum-ion batteries as well.     

Calculated vibrational structure of the first band of the photoelectron spectrum of HO 2 − and the electron affinity of HO2

The vibrational structure of the first band of the photoelectron (PE) spectrum of HO ₂ ^? and DO ₂ ^? has been calculated on the basis of (slightly modified) ab initio potentials. The best agreement with the experimental spectrum of HO ₂ ^? is obtained for a vibrational temperature of ca. 600 K. “Peak D”, which has been under debate in earlier work, is composed of two transitions, with the “hot” transition 3 ₁ ¹ being more intense than the adiabatic transition. Since thev ₂ bending mode of DO₂ has significant OO stretching character, the vibrational structure of the PE spectrum of DO ₂ ^? is more complex than that of HO ₂ ^? . Large-scale RCCSD(T) calculations of the equilibrium electron affinity of HO₂ yield 1.058 eV which agrees with the experimental value of 1.044 ± 0.020 eV.     

The vibrational spectrum and the conformation of the P2O4−7 anion in Fe2P2O7

The infrared and Raman spectra of Fe₂P₂O₇ have been recorded and discussed. The results point to a bent bridge conformation and to a centrosymmetric space group. They make it possible to solve some discrepancies arising from contradictory results formerly reported by two independent crystallographic studies.     

Progress in the non-equilibrium vibrational kinetics of hydrogen in magnetic multicusp H− ion sources

The non-equilibrium vibrational kinetics of H₂ in multicusp magnetic discharges has been studied by improving a previous model developed by our groups. In particular, a complete set of V-T (vibrational translation) rates involving H-H₂(v) collisions, calculated by using a three-dimensional dynamics approach, has been inserted into our self-consistent model for better representing the corresponding relaxation. Different experimental situations are simulated with special emphasis on the temporal scales necessary for the different distributions (electron energy and vibrational distributions) to reach stationary values. Finally, a comparison between theoretical and experimental quantities such as vibrational temperature, electron temperature, electron number density and concentration of negative ions (H⁻) shows a satisfactory agreement, thus indicating the basic correctness of our model.     

The thermodynamic stability of the LaBr 4 − ion

The thermodynamic stability of the LaBr ₄ ^? anion was for the first time studied by high-temperature mass spectrometry and nonempirical quantum-chemical methods. The experimental and theoretical enthalpies of the reaction $ LaBr_4^ - = Br^ - + LaBr_3 The thermodynamic stability of the LaBr₄⁻ anion was for the first time studied by high-temperature mass spectrometry and nonempirical quantum-chemical methods. The experimental and theoretical enthalpies of the reaction were Δ_r H°(298.15 K) = 302 ± 14 and 303 kJ/mol, respectively. The value Δ_f H° (LaBr₄⁻, g, 298.15 K) = −1105 ± 14 kJ/mol was recommended as the enthalpy of formation of the LaBr₄⁻ anion. Original Russian Text ? M.F. Butman, L.S. Kudin, V.B. Motalov, D.A. Ivanov, V.V. Sliznev, K.W. Kr?mer, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 5, pp. 885–890.     

Detection of vibrational bending mode ν8 and overtone bands of the propargyl radical, HCCCH2 X̃ 2B1

Infrared (IR) absorption spectra of matrix-isolated HCCCH(2) have been measured. Propargyl radicals were generated in a supersonic pyrolysis nozzle, using a method similar to that described in a previous study (Jochnowitz, E. B.; Zhang, X.; Nimlos, M. R.; Varner, M. E.; Stanton, J. F.; Ellison, G. B. J. Phys. Chem. A 2005, 109, 3812-3821). Besides the nine vibrational modes observed in the previous study, this investigation detected the HCCCH(2) X? (2)B(1) out-of-plane bending mode (ν(8)) at 378.0 (±1.9) cm(-1) in a cryogenic argon matrix. This is the first experimental observation of ν(8) for the propargyl radical. In addition, seven overtone and combination bands have also been detected and assigned. Ab initio coupled-cluster anharmonic force field calculations were used to guide the analysis. Furthermore, ν(12), the HCCCH(2) in-plane bending mode, has been assigned to 333 (±10) cm(-1) based on the detection of its overtone (2ν(12), 667.7 ± 1.0 cm(-1)) and a possible combination band (ν(10) + ν(12), 1339.0 ± 0.8 cm(-1)). This is the first experimental estimation of ν(12) for the propargyl radical.     

Solid State Chemistry of A4B3−Molecules

Abstract

The system P₄S₃?P₄Se₃?As₄S₃?As₄Se₃ was investigated by thermal and X-ray methods. Five regions of solid solubility with different crystal structures were found. All transform at higher temperatures into the plastically-crystalline state with β-P₄S₃?structure.

The substituted species P_4-nAs_nS_mSe_3-m (n = 0–4, m = 0–3) are formed in molten mixtures of A₄B₃?molecules (FIGURE 1). They were identified by HPLC and mass-spectrometric measurements.

After long equilibration times P₄Se₃, As₄S₃ and As₄Se₃ decompose peritectoidally into the resp. A₄B₄?species and an amorphous product.     

Effect of EDTA on the diffusion behavior of 99TcO4 − and ReO4 − in GMZ bentonite

Polyaminopolycarboxylate EDTA with powerful metal-binding property, which often presents in low and intermediate-level waste, can enhance the radionuclide migration. The effect of EDTA on the diffusion behavior of ⁹⁹TcO₄ ^? and ReO₄ ^? in Gaomiaozi (GMZ) bentonite was investigated by using through-diffusion method. For ⁹⁹TcO₄ ^? in present of EDTA, the D _e values was (1.2 ± 0.1) × 10^?11 m²/s, which was 4 times higher than that in absent of EDTA. It can be explained that the complexation between ⁹⁹TcO₄ ^? and EDTA might be formed. By contrast, the D _e values of ReO₄ ^? remained unchanged in present or absent of EDTA, indicating that ReO₄ ^? could not complex with EDTA. However, the diffusion of ReO₄ ^? could be increased in present of EDTA, the D _a value was found to be increased from 1.8 × 10^?10 to 5.4 × 10^?10 m²/s. It demonstrated that ReO₄ ^? need more drastic conditions to form the Re(VII)–EDTA complexes than those used for ⁹⁹TcO₄ ^?. For both ReO₄ ^? and ⁹⁹TcO₄ ^?, the rock capacity factor α is less than the total porosity ε _tot, indicating that they has little retention/sorption on the surface of bentonite.     

Ab initio second-order Møller-Plesset calculation of the vibrational spectra of C4 clusters

Second-order Møller-Plesset calculations on the C₄ potential surface yielded three isomers, a linear triplet and rhombic and tetrahedral singlets. A large discrepancy between observed and calculated frequencies of the Σ_u⁺ vibration of linear ¹²C₄ is outside the expected range of error. It is tentatively suggested that an observed absorption at 1544 cm⁻¹ previously assigned to C₅ might belong instead to C₄.     

The vibrational spectra of germane and silane derivatives—XII. A reassignment of the dimethylhalosilanes

The i.r. and Raman spectra of the dimethylhalosilanes, Me₂SiHZ and Me₂SiDX (X = F, Cl, Br, I) have been recorded and the fundamental vibrations assigned. Analysis of the spectra of the deuterated compounds indicate that existing assignments for Me₂SiHX are in error.