An investigation of vibrational exciton bands in solid nitrous oxide

Infrared spectra of N₂O crystals containing dilute to isotopic impurities are reported. Information on the second moments and other properties of the vibrational exciton bands has been determined from an analysis of the impurity modes, the LOTO splittings, and a comparison of the transition dipole moments of N₂O with those of CO₂. The effect of the random sense of the molecules on the spectra is discussed.     

Tungsten oxide bronzes with alkali metals

Single-phase samples of tungsten bronzes M _x WO₃ (M = K⁺, Rb⁺, Cs⁺) are prepared by solid-state synthesis. The reversibility of the M_0.33WO₃/M⁺-solid electrolyte interface is studied subject to the alkali metal nature and humidity over a wide temperature interval. The exchange current density at 24°C and 58%-relative humidity is 3.6 × 10^?4 A/cm² for the Rb_0.33WO₃/Rb⁺-solid electrolyte interface; 2.2 × 10^?4 A/cm² for the Cs_0.33WO₃/Cs⁺-solid electrolyte interface; and 1.3 × 10^?4 A/cm² for the K_0.33WO₃/K⁺-solid electrolyte interface. A correlation between the reversibility of the bronze|solid electrolyte interface, which is characterized by the exchange current density, and the rate of potential equilibration in sensor systems, where the bronze is a reference electrode, is revealed. Ionic component of the conductivity of the synthesized tungsten oxide bronzes is measured at a background of the predominant electronic conductivity. The ionic conductivity is three orders of magnitude lower than the electronic conductivity; it decreases in the series Rb_0.33WO₃ > Cs_0.33WO₃ > K_0.33WO₃, amounting to 2.3 × 10^?2, 2.1 × 10^?3, and 2 × 10^?4 S cm^?1, respectively. The working capacity of the M_0.3WO₃ bronzes as reference electrodes in sensor systems for carbon dioxide detection is evaluated. The plots of the cell potential vs. the CO₂ concentration in the electrochemical cells are linear, their slopes (59 ± 1 mV/decade) are characteristic for one-electron process. The fastest response to changes in the CO₂ concentration was obtained with the sensor system that used Rb_0.33WO₃ as reference electrode.     

Solvent-free MALDI investigation of the cationization of linear polyethers with alkali metals

The MALDI technique with solvent-free sample preparation has been applied to evaluate relative gas-phase affinities of polyether chain polymers with alkali metal cations. The study is performed on poly(ethylene glycol) and poly(propylene glycol) polymers of different lengths (PEG600, PEG1000, PPG425, PPG750) and the alkali metal cations Li(+), Na(+), K(+), and Cs(+). The experiments show that the lattice energy of the alkali metal salts employed as cation precursors can have a strong influence on the outcome of conventional MALDI measurements. With the solvent-free method, these crystal binding effects can be made negligible by combining in the same sample alkali metal salts with different counterions. The recorded MALDI spectra show that the polyether-cation aggregation efficiencies decrease systematically with growing cation size. This cation size selectivity is considerably enhanced for the polymers with the shorter chains, which can be attributed to the reduced ability of the polymer to build a coordination shell around the larger cations. The steric effects introduced by the side CH3 group of propylene glycol with respect to ethylene glycol also enhance the preference for cationization of the polymer by the smaller cations. These observations correct some qualitative trends derived from previous studies, which did not account for lattice energy effects of the cation precursors.     

Iron-catalyzed propylene epoxidation by nitrous oxide: studies on the effects of alkali metal salts

SBA-15-supported iron catalysts with and without alkali metal salt modifications were studied for propylene oxidation by nitrous oxide. The reaction route could be dramatically changed from allylic oxidation to epoxidation by modification of the FeOx/SBA-15 catalyst with alkali metal salts. The KCl-1 wt % FeOx/SBA-15 (K/Fe = 5) catalyst exhibited the best catalytic performances for propylene epoxidation, over which ca. 50% propylene oxide selectivity could be gained at a 10% propylene conversion at 648 K. Characterizations with diffuse reflectance UV-Vis, XANES, and Raman spectroscopic techniques revealed that the modification with KCl increased the dispersion of the iron species and changed the local coordination of iron into a tetrahedral configuration on the inner surface of SBA-15. This tetrahedrally coordinated iron site, which was probably stabilized by potassium ions, was proposed to account for the epoxidation of propylene by nitrous oxide. At the same time, the reactivity of lattice oxygen was inhibited, and the acidity of the FeOx/SBA-15 was eliminated. These changes should also contribute to the increase in the selectivity to propylene oxide. The counteranions in the alkali metal salts exerted a significant influence on the catalytic behaviors probably via an electronic effect.     

An investigation of the dark formation of nitrous acid in environmental chambers

The formation of nitrous acid (HONO) in the dark from initial concentrations of NO₂ of 0.1–20 ppm in air, and the concurrent disappearance of NO₂, were monitored quantitatively by UV differential optical absorption spectroscopy in two different environmental chambers of ca.4300- and 5800-L volume (both with surface/volume ratios of 3.4 m^?1). In these environmental chambers the initial HONO formation rate was first order in the NO₂ concentration and increased with the water vapor concentration. However, the HONO formation rate was independent of the NO concentration and relatively insensitive to temperature. The initial pseudo-first-order consumption rate of NO₂ was (2.8 ± 1.2) × 10^?4 min^?1 in the 5800-L Teflon-coated evacuable chamber and (1.6 ± 0.5) × 10^?4 min^?1 in a 4300-L all-Teflon reaction chamber at ca.300 K and ca.50% RH. The initial HONO yields were ca.40–50% of the NO₂ reacted in the evacuable chamber and ca.10–30% in the all-Teflon chamber. Nitric oxide formation was observed during the later stages of the reaction in the evacuable chamber, but ca.50% of the nitrogen could not be accounted for, and gas phase HNO₃ was not detected. The implications of these data concerning radical sources in environmental chamber irradiations of NO_x? organic-air mixtures, and of HONO formation in polluted atmospheres, are discussed.     

On the use of nitrous oxide and ethylene for gas phase dosimetry

The absolute yield value G(H₂) = 1·36±0·07 for ethylene radiolysis was determined. Ethylene, unlike nitrous oxide, is convenient for dosimetry if small irradiation cells are used.     

Tuning the work function of ultrathin oxide films on metals by adsorption of alkali atoms

We report a theoretical investigation of the adsorption of alkali metal atoms deposited on ultrathin oxide films. The properties of Li, Na, and K atoms adsorbed on SiO(2)/Mo(112) and of K on MgO / Ag(100) and TiO(2)/Pt(111) have been analyzed with particular attention to the induced changes in the work function of the system, Phi. On the nonreducible SiO(2) and MgO oxide films there is a net transfer of the outer ns electron of the alkali atom to the metal substrate conduction band; the resulting surface dipole substantially lowers Phi. The change in Phi depends (a) on the adsorption site (above the oxide film or at the interface) and (b) on the alkali metal coverage. Deposition of K on reducible TiO(2) oxide films results in adsorbed K(+) ions and in the formation of Ti(3+) ions. No charge transfer to the metal substrate is observed but also in this case the surface dipole resulting from the K-TiO(2) charge transfer has the effect to considerably reduce the work function of the system.     

Determination of alkali metals in control and AD brain samples by different techniques

Several metals are suspected or known to be involved in neurological disorders such as Alzheimer's disease (AD), therefore, elemental distribution studies have received intense attention for years. The present work focuses on a group of lesser studied elements in this context, alkali metals.Previously, an adequate neutron activation analysis (NAA) method has been developed and applied successfully for the determination of Na, K, Rb and Cs in brain samples of control subjects. This work has been extended to include AD patients, so that average values, distribution patterns and interpersonal variability could be compared and possible correlation between control and AD data could be studied.Despite the merits of the technique, its drawbacks are evident. Therefore, applicability of rapid spectrochemical methods as alternatives has been investigated. ICP-AES has been used for analysis of Li, Na and K. No interferences were observed, but ultrasonic nebulisation was needed for Li quantification. Rb and Cs were measured by ICP-MS with In as internal standard. Agreement between different techniques is found to be good for Na, K and Rb, while Cs values show somewhat higher differences.     

The minimal energy conformations of o-benzosemiquinone anion radicals in the solvents containing the alkali metals and the alkali earth metals

The minimal energy conformations of o-benzosemiquinone anion radicals in the solvents containing the alkali metals and the alkali earth metals were calculated by using the INDO method and the molecular geometry adjusting method. Our previous calculations of o-benzosemiquinone anion radical in the lithium ion solution showed that the total energy of the minimal energy conformation in the case of the assignment |A₃| > |A₄| were lower by approximately 320 kcal/mol than that in the case of the assignment |A₃| > |A₄|. Therefore, the calculations of the minimal energy conformations of o-benzosemiquinone anion radicals in the metal ion solutions were carried out in the cases of the assignment |A₃| > |A₄|. The conformations in both assignments A₃ < A₄ < 0 and (A₃ < 0 < A₄ and |A₃| > |A₄|) were calculated. Although the metal ions were not explicitly contained in the molecular geometries, the minimal energy conformations are considered to be close to the real minimal energy conformations of o-benzosemiquinone anion radicals in the metal ion solutions. The C? O bond lengths has a good positive rank correlation with the stabilities of o-benzosemiquinone radicals in the divalent metal ion solutions and the bond angles ∠C₃C₄H₄ had a good negative rank correlation with those stabilities.     

Synthesis of pyroperoxoniobates of the alkali metals

Conclusions A new method for obtaining pyroperoxoniobates of the alkali metalswith the composition(Na, K)₄Nb₂O₁₁ · 2H₂O has been developed.The solid salts (Na, K)₄Nb₂O₁₁ · 2H₂O are stable above 100°. They decompose completely 300° with the formation of pyro salts having the composition (Na, K)₄Nb₂O₇ of reagent purity.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1281–1283, July, 1966.     

Calculated anisotropies in the fermi surface of alkali metals

The densities of states and Fermi energies were accurately calculated from E(k) data obtained by the self-consistent-band Augmented Plane Wave (APW ) method, using a quadratic energy expansion. The reliability of the Monte Carlo integration was investigated. It was sufficiently good to determine the anisotropy of the Fermi surface of lithium, sodium, and potassium.