Reactive scattering of alkali dimers K2 + I2, CH2I2, CHI3, CBr4

Angular distribution measurements of KX reactive scattering of a potassium dimer K₂ beam by I₂ and by a series of halomethane molecules are reported. The K₂ + I₂ reactive scattering is similar to that previously observed for K₂ + Br₂. The predominant reaction path yields K + KI + I with the K and KI product recoiling in the forward direction. However, the forward peak of the KI differential cross section is lower than that for K from K₂ + I₂ and is broader than that observed for KBr from K₂ + Br₂. This is attributed to slow dissociation of the I ₂ ^- ion formed in the electron jump mechanism previously proposed for K₂ + Br₂. In the halomethane reactions, both alkali atoms of the K₂ dimer become bound alkali halide molecules in all reactive collisions, despite the direct dynamics of the corresponding supersonic K atom reactions. Thus, these reactions provide compelling evidence for a second electron jump mechanism, previously proposed for the reactions of K₂ dimers with polyhalide molecules. The differential cross sections for the K₂ dimer plus halomethane reactions indicate an osculating collision complex with a lifetime at least comparable to its rotational period, perhaps much longer. This reaction complex is identified with the doubly ionic state formed by the second electron jump transition.     

Semiempirical pseudopotential surfaces for chemical reactions: The (AB)+ X - dialkali halide systems

A generalization of the Roach-Child semiempirical pseudopotential calculation for K + NaCl to several analogous dialkali halide systems has been used to elucidate the chemical interactions governing the reaction dynamics. The Li + LiF ground-state potential surface, which exhibits a ～ 20 kcal/mole basin for isosceles Li₂F, is qualitatively similar to one obtained in a recent configurational interaction calculation. It is shown that regions of the Na₂Cl ground-state surface corresponding to Na₂ ⁺ interacting with Cl^- can be described in terms of an ion-pair Rittner potential model similar to that employed for the alkali halides. Chemical trends in the triangular complex well depths satisfactorily account for the experimentally observed transition between the collision complex mechanism (Rb + KCl) and the osculating complex model (Li + KBr) for the alkali-alkali halide exchange reactions at thermal energies. For collinear configurations with the alkalis on opposite ends, avoided intersections between the lowest two potential surfaces are characterized in terms of diabatic surfaces computed from truncated basis sets. Crossings of these surfaces account for the vibrational-electronic energy transfer between alkali atoms and vibrationally excited alkali halides. The ionic X ^- + A ₂ ⁺ potential surfaces are used to predict the product electronic excitation and partitioning of exoergicity in reactions of halogen atoms with alkali dimer molecules.     

Investigation of the local structure of Cu2+ ions doped in alkali lead tetraborate glasses by their electron paramagnetic resonance and optical spectra

The local structure of the Cu²⁺ centers in alkali lead tetraborate glasses was theoretically studied based on the optical spectra data and high-order perturbation formulas of the spin Hamiltonian parameters (electron paramagnetic resonance g factors g_∥, g_⊥ and hyperfine structure constants A_∥, A_⊥) for a 3d⁹ ion in a tetragonally elongated octahedron. In these formulas, the relative axial elongation of the ligand O^2? octahedron around the Cu²⁺ due to the Jahn–Teller effect is taken into account by considering the contributions to the g factors from the tetragonal distortion which is characterized by the tetragonal crystal-field parameters Ds and Dt. From the calculations, the ligand O^2? octahedral around Cu²⁺ is determined to suffer about 19.2% relative elongation along the C₄ axis of the alkali lead tetraborate glass system, and a negative sign for A_∥ and a positive sign for A_⊥ for these Cu²⁺ centers are suggested in the discussion.     

Improved luminescence of Y2MoO6:Eu3+ by doping Li+ ions for light-emitting diode applications

The photoluminescence (PL) property of Y₂MoO₆:Eu³⁺ doped with Li⁺ is investigated in this paper. The red luminescence of Eu³⁺ in Y₂MoO₆ lattice has greatly enhanced by codoping monovalent alkali metal ions Li⁺ into the lattice. The drastic increase in the luminescence intensity of Y_2?xLi_xMoO₆:Eu³⁺ originates from the reason that the Li⁺ ions may serve as a self-promoter for better crystallization to reduce the defect or as a lubricant for the complete incorporation of the Eu³⁺ ions into the Y₂MoO₆ host.     

Thermally stimulated depolarization of Eu2+-cation vacancy dipoles in alkali halide single crystals

Ionic thermocurrent (ITC) measurements have been performed on eight alkali halide single crystals doped with divalent europium. In all cases, the observed ITC peaks were fitted with a mono-energetic model without to appeal to any dipole-dipole interaction. Values for the reorientation parameters have been calculated. The relationship T_M1nτ^?1 α E previously found for I–V complexes in alkali halides has been found to be very well obeyed for the experimental data obtained in this investigation. It is also reported that the logarithm of the experimentally determined energies for free dipole reorientation shows a linear dependence on the interaction distance between the Eu²⁺ ion and the surrounding halogen ions in the distorted cubic site occupied by this impurity in the alkali halides.     

Pb2+ Defects in perovskite-like KMgF3 crystals

Abstract

The physical properties of Pb²⁺ impurities in the perovskite-like lattice of KMgF₃ are very similar to those of (ns)² ions in alkali halides. The impurity inhomogeneous distribution leads to high dopant levels in the bottom region of the crystals, with a segregation coefficient equal to 0. 020. The optical features of the 336 nm emission support its attribution to luminescence of Pb²⁺ ions from the relaxed excited B state.     

A new force field for the adsorption of H2, O2, N2, CO,H2O,and H2S gases on alkali doped carbon nanotubes

The main goal of this work is the generation of a new force field data set to the interaction of several gases such as H₂, O₂, N₂, CO, H₂O, and H₂S with alkali cation-doped carbon nanotubes (CNTs) using ab initio calculations at the MP2(full)/6-311++G(d,p) level of theory. Different alkali cations including Li⁺, Na⁺_, K⁺ and Cs⁺ were used to dope in the CNT. The calculated potential energy curve for the interaction of each gas molecule with each alkali cation-doped CNTs was fitted to an analytical potential function to obtain the parameters of the potential function. A modified Morse potential function was selected for the fitting in which the electrostatic interactions has been accounted by adding the β/r term to the Morse potential. The accuracy of the calculated force field was checked via Grand Canonical Monte Carlo (GCMC) simulation of the H₂ adsorption on Li-doped graphite and Li-doped CNT. The results of these simulations were compared with the experimental measurements and the closeness of the simulation results with the experimental data indicated the accuracy of the proposed force field. The main merit of this work is the derivation of a specific force field for interaction of each of six gases with four alkali cation-doped CNT, which can be used in molecular simulation of these 24 of systems. The simulation results showed the increase of the H₂ adsorption capacity of nanotube and graphite up to 50% and 10%, respectively, due to the insertion of Li ions.     

Effect of Li2O content on physical and structural properties of vanadyl doped alkali zinc borate glasses

The effect of Li₂O content in vanadyl doped 20ZnO+xLi₂O+(30−x)Na₂O+50B₂O₃ (5≤x≥25) glasses has been studied with respect to their physical and structural properties. The absence of sharp peaks in XRD spectra of these glass samples confirms the amorphous nature. The physical parameters like density, refractive index, ionic concentration and electronic polarizability vary non-linearly with x mol% depending on the diffusivities of alkali ions. EPR and optical absorption spectra reveal that the resonance signals are characteristics of VO²⁺ ions in tetragonally compressed octahedral site. Spin-Hamiltonian, crystal field, tetragonal field and bonding parameters are found to be in good agreement with the other reported glass systems. The tetragonal distortion (g_⊥-g_∥) and Dt reveals that their values vary non-linearly with Li₂O content and reaches a minimum at x=10 mol%. An anomaly of character has been observed in all the properties of vanadyl doped glass systems, which gives a clear indication of mixed alkali effect.     

Third-order elastic constants for 2:2 chalcide crystals possessing the sodium chloride structure

Third-order elastic constants of 45 chalcide crystals having the sodium chloride structure are reported using Born-Mayer potential model. We have considered repulsive interaction up to second nearest neighbours. The temperature coefficients of the third-order elastic constants have also been computed for these crystals. As is the case for NaCl-type alkali halides we find that C₁₁₁, C₁₁₂, C₁₆₆ are negative and C₁₄₄ are positive for 2:2 chalcide crystals possessing the NaCl-type structure. We have found that a₁₂₃, a₄₅₆ and a₁₄₄ are negative whereas a₁₁₂ and a₁₆₆ are positive, once again in agreement with the situation found for the alkali halides a₁₁₁ values are positive for alkali halides whereas they are both positive and negative depending upon the interionic distance for the chalcide crystals. We have found that the nature of the variation of C⁰_αβγ with interionic separation is similar for alkali halides and for the 2:2 chalcides having the NaCl-structure. We have also computed the values of the pressure derivatives of second-order elastic constants for MgO, CaO, and SrO which agree well with the experimental values indicating the satisfactory nature of our computed data for C_αβγ.     

Effect of alkali ions on the strength development of cement paste by Mössbauer spectrometry

Two clinker raw mixtures (83 wt% limestone +12 wt% clay +5 wt% α-Fe₂O₃) were fired at 1150°C for three hours in open furnace, each with 100 wt%-in addition-of an alkali carbonate (Na₂CO₃ and K₂CO₃) respectively. Each produced cliker was mixed with 5 wt% natural gypsum to produce portland cement, then with 25 wt% tap water. Compressive strength, ultrasonic pulse test, X-ray diffraction and Mossbauer effect measurements were carried out each at different times of hydration (21, 28 and 45 days). The effect of alkali ions on the strength development of cement pastes is discussed, the accuracy of Mössbauer, spectrometer in determining the cement strength is demonstrated.     

Role of monovalent alkali ions in the Yb3+ centers of CaF2 laser crystals

Yb³⁺ and M⁺ monovalent alkali ions (M⁺ = Li⁺, Na⁺, K⁺)-co-doped CaF₂ cubic laser crystals were grown by the micro-pulling-down method (μ-PD) under CF₄ atmosphere. Structural and spectroscopic characterizations of Yb³⁺ in substitution of Ca²⁺ (absorption, emission and decay curves) were carried out to study the effect of M⁺ ions as charge compensators.     

Radiolysis of ferrous ammonium sulphate in alkali nitrate and alkali halide matrices

Radiolysis of ferrous ammonium sulphate (FAS) dispersed in (a) alkali nitrates [KNO₃, NaNO₃, Ba(NO₃)₂, CO(NH₃)₆(NO₃)₃] (b) alkali halides [KCl, KBr] and (c) binary mixtures of above [KNO₃ + KCl, Ba(NO³)₂ + BaCl₂) has been extensively investigated. FAS becomes oxidized and Fe³⁺ formation seems to depend upon the nitrate concentration and gamma dose but is independent of halide concentration. Mossbauer studies confirm these findings and it appears that basic ferric sulphate may be formed during the oxidation process.     

Spectroscopic properties, energy transfer and structural analysis of Sr2CeO4:M+ and Sr2CeO4:Eu3+, M+ (M+ = Li+, Na+, K+)

The room-temperature luminescent emission characteristics of Sr₂CeO₄:M⁺ and Sr₂CeO₄:Eu³⁺,M⁺ (M⁺ = Li⁺, Na⁺, K⁺) have been investigated under UV excitation. By introducing appropriate alkali metal cations dopants (Li⁺, Na⁺, K⁺) into the crystalline lattice, not only emission color of the blue-white-emitting Sr₂CeO₄ doped with low Eu³⁺ content can be tuned to green, but also the red emission intensity of Sr₂CeO₄ doped with high Eu³⁺ concentration is strengthened significantly. The relevant mechanisms have been elucidated in detail.     

Reactive scattering of alkali dimers: K2 + HgCl2, HgBr2, HgI2

Angular distribution measurements of KX reactive scattering of a potassium dimer K₂ beam by mercuric halide molecules HgX₂ are reported. All the reactions exhibit strong forward peaking in the centre of mass differential cross sections and large total reaction cross sections Q_r ～ 150 Ų. However, there is substantial backward peaking ( forward peak) for HgBr₂, HgI₂. Despite the direct stripping dynamics, both alkali atoms of the K₂ dimer become bound alkali halide molecules in most (perhaps all) reactive collisions. A major fraction of the reaction exoergicity is disposed into vibrational excitation of the product KX molecules. A mechanism involving a first electron jump in the entrance valley and a second electron jump in the exit valley of the potential surface is suggested to explain the rapid transfer of both K₂ valence electrons.     

X-ray spectra and specific features of the structure of lithium-sodium cobaltite Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Na<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>CoO<Subscript>2</Subscript>

The electronic structure and specific features of the structure of nonstoichiometric cobaltite Li _x Na _y CoO₂ (x = 0.42, y = 0.36) have been studied comprehensively. The calculated multiplet for the lowspin state of the Co³⁺ ion agrees with the experimental spectra. It has been established using X-ray absorption spectra measured in the total photoelectric effect yield and total fluorescence yield modes that the Li _x Na _y CoO₂ cobaltite is stoichiometric with respect to the alkali metal near its surface and is defective inside. It has been demonstrated that the charge compensation in the case of an alkali metal deficit in LixNayCoO₂ is due to holes in O 2p states.     

Etude par R.P.E. d'electrolytes vitreux appartenant au systeme B2O3-Li2O-LiCl

An EPR study of fast Li⁺ ion vitreous conductors belonging to the B₂O₃-Li₂O-LiCl system has been carried out. The samples have been subjected to X-ray irradiation at room temperature. Two types of paramagnetic centers have been observed. The first one is the Cl₂^- species (Vk center) present in the part of the vitreous domain which corresponds to low LiCl concentrations, it vanishes when Li⁺ and Cl^- begin to order. The second one is of the B.O.H.C. type often present in alkali borate glasses. Its presence shows the similarity between the boron-oxygen network of the alkali borate glasses and of our samples containing alkali chloride.     

A Sensitive Schiff-Base Fluorescent Chemosensor for the Selective Detection of Zn2+

A Schiff-base fluorescent probe – N, N^/-bis(salicylidene) trans 1, 2 – diaminocyclohexane (H ₂ L) was synthesized and evaluated as a chemoselective Zn²⁺ sensor. Upon treatment with Zn²⁺, the complexation of H ₂ L with Zn²⁺ resulted in a bathochromic shift with a pronounced enhancement in the fluorescence intensity in ethanol solution. Moreover, other common alkali, alkaline earth and transition metal ions failed to induce response or minimal spectral changes. Notably, this chemosensor could distinguish clearly Zn²⁺ from Cd²⁺. The stoichiometric ratio and association constant were evaluated using Benesi – Hildebrand relation giving 1:1 stoichiometry. This further corroborated 1:1 complex formation based on Job’s plot analyses.     

The electrochemical insertion properties of sodium vanadium fluorophosphate,Na3V2(PO4)2F3

The structural and alkali ion insertion characteristics of sodium vanadium fluorophosphate, Na₃V₂(PO₄)₂F₃ are presented. The material was prepared using a solid-state carbothermal reduction approach involving the precursors VPO₄ and NaF. Electrochemical characterization of the Na₃V₂(PO₄)₂F₃ phase in the potential range 3.0–4.6 V vs. Li, revealed a structured voltage response corresponding to the reversible cycling of two alkali ions per formula unit. The associated specific capacity was around 120 mAh/g, at an average discharge voltage of around 4.1 V vs. Li. The stability of the alkali ion insertion reactions was confirmed by long term cycling experiments, which demonstrated low capacity fade over the initial 220 cycles. Voltage excursions to 5 V vs. Li suggest that all three Na ions may be successfully extracted from the fluorophosphate phase, although this process is likely accompanied by some concurrent structural degradation.     

High pressure effect on structural and spectroscopic properties of Sm3+-doped alkali silicate glasses

Structural and spectroscopic properties of Sm³⁺-doped alkali silicate glasses were investigated after densification at 7.7?GPa in a large volume high pressure apparatus. The glass composition was 33M₂O?+?66SiO₂?+?1Sm₂O₃, where M?=?Li, Na or K. Raman and infrared spectroscopy revealed small changes in the vibrational modes dependent on the alkali ion. Irreversible changes were observed in the optical absorption spectra of Sm³⁺ ions. The Judd–Ofelt parameters were calculated to evaluate the effect of pressure on the local field. For lithium silicate, Ω₂ parameter increased, suggesting the densification increased the local asymmetry of the Sm³⁺ environment. For sodium silicate, this parameter decreased considerably, suggesting the opposite effect on the local field, while for potassium silicate, it remained practically unchanged. The changes induced by high pressure are probably due to the irreversible changes in the distances and bond angles between the rare earth ion and the ligands.     

Coumarin Based Fluorescent Probe for Colorimetric Detection of Fe<Superscript>3+</Superscript> and Fluorescence Turn On-Off Response of Zn<Superscript>2+</Superscript> and Cu<Superscript>2+</Superscript>

A new coumarin based Schiff-base chemosensor-(E)-7-(((8-hydroxyquinolin-2-yl)methylene) amino)-4-methyl-2H-chromen-2-one (H ₁₁ L) was synthesized and evaluated as a colorimetric sensor for Fe³⁺ and fluorescence “turn on-off” response of Zn²⁺ and Cu²⁺ using absorption and fluorescence spectroscopy. Upon treatment with Fe³⁺ and Zn²⁺, the absorption intensity as well as the fluorescence emission intensity increases drastically compared to other common alkali, alkaline earth and transition metal ions, with a distinct color change which provide naked eye detection. Formation of 1:1 metal to ligand complex has been evaluated using Benesi-Hildebrand relation, Job’s plot analyses, ¹H NMR titration as well as ESI-Mass spectral analysis. The complex solution of H ₁₁ L with Zn²⁺ ion exhibited reversibility with EDTA and regenerate free ligand for further Zn²⁺ sensing. H ₁₁ L exhibits two INHIBIT logic gates with two different chemical inputs (i) Zn²⁺ (IN1) and Cu²⁺ (IN2) and (ii) Zn²⁺ (IN1) and EDTA (IN2) and the emission as output. Again, an IMPLICATION logic gate is obtained with Cu²⁺ and EDTA as chemical inputs and emission as output mode. Both free ligand as well as metal-complexes was optimized using density functional theory to interpret spectral properties. The corresponding energy difference between HOMO-LUMO energy gap for H ₁₁ L, H₁₁L-Zn²⁺ and H₁₁L-Cu²⁺ are 2.193, 1.834 and 0.172 eV, respectively.