7440-09-7

Through a three-level kinetic model, the branching ratio of the nascent photofragment K in the 52PJ fine-structure states following photodissociation of KI by a 193 nm excimer laser has been experimentally determined to be K(52P3/2) = 0.791 and K(52P1/2) = 0.209 with +/- 1percent accuracy.The model has taken into account the rapid energy transfer between the 52PJ doublets and the result appears to be more accurate than those fluorescence intensity ratio measurements under low pressure condition.The cross section of fine structure mixing induced by H2 collisions has also been measured to be 134 +/- 6 Angstroem2 for the transition 52P3/2 2P1/2 and 72 +/- 5 Angstroem2 for its reverse process.The ratio 1.86 is consistent with the value 1.89 predicted by principle of detailed balance.Using the Stern-Volmer equation, we have also obtained the radiative lifetime 137 +/- 4 ns for the K(52PJ) state and its quenching cross section 10.4 +/- 1.8 Angstroem2 by collision with H2 molecule.The latter appears much smaller than those of fine-structure energy transfer processes by an order of magnitude.

Two phases in the binary system K/N have been obtained via co-deposition of potassium and nitrogen onto polished sapphire at 77 K and subsequent heating to room temperature. The powder diffraction pattern of one of these phases can be satisfactorily interpreted by assuming the composition K3N, and the anti-TiI3 structure-type, which is also adopted by Cs 3O. The resulting hexagonal lattice constants are: a = 779.8(2), c = 759.2(9) pm, Z = 2, P63/mcm. Comparison with possible structures of K3N generated by computational methods and refined at Hartree-Fock- and DFT level, reveals that the energetically most favoured structure has not formed (presumable Li3P-type), but instead one of those with very low density. In this respect, the findings for K3N are analogous to the results on Na3N. The thermal evolution of the deposited starting mixture has been investigated. Hexagonal K3N transforms to another K/N phase at 233 K. Its XRD can be fully indexed resulting in an orthorhombic cell a = 1163, b = 596, c = 718 pm. Decomposition leaving elemental potassium as the only residue occurs at 263 K.

The unimolecular dissociation of metastable photoionized mass-selected heterogeneous alkali clusters is investigated using a tandem time-of-flight spectrometer.NaK+n and NanK+ are found to dissociate by evaporation of either a single neutral atom or a neutral dimer of the most abundant constituant.This behavior differs from the evaporation of heterogeneous neutral clusters which might always evaporate potassium in order to explain the sodium enrichment in the NaxKy neutral cluster distributions.This difference in the dissociation patterns of neutral and ionic heterogeneous clusters puts into evidence the influence of the charge in unimolecular dissociation processes.

The real time electrodeposition of potassium has been monitored for the first time in an ionic liquid using in situ electrodeposition-X-ray photoelectron spectroscopy (XPS). The ionic liquid used was N-butyl-N- methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpyrr] [NTf2]), and electrodeposition occurred at a nickel mesh electrode. Potassium electrochemistry was monitored at the ionic liquid-vacuum-electrode interface using a novel cell design.

Pulsed photodissociation of KJ at 193 nm was used as the source of K(52PJ) in a series of experimental studies of collisional deactivation.By comparison of the yield of ground-state K(42S1/2) in the presence and absence of H2 and D2, it was possible to demonstrate that chemical reaction plays no significant role in the deactivation process.Of the available quenching channels, that leading to the intermediate 52S1/2 and 32DJ states appears to dominate.The possible importance of near-resonant electronic-to-vibrational energy transfer is discussed and an application to the refinement of alkali metal lasers presented.

The absolute third-order rate constant for the reaction K+I+He->KI+He has been measured directly by monitoring atomic iodine under pseudo-first-order conditions in the presence of excess atomic potassium, derived from a heat pipe oven, and helium.I(52P3/2) was generated by the repetitive pulsed irradiation of KI vapor and studied by time-resolved resonance fluorescence at λ=178.3 nm (I(5p46s(2P03/2))) using photon counting and signal averaging.K(42S1/2 was monitored in steady mode by resonance fluorescence of the Rydberg transition at λ=404 nm (K(52PJ)-K(42S1/2)) using phase-sensitive detection.We report the third-order rate constant of k1(T=567 K)=(3.04+/-0.73)x10-31 cm6 atom-2 s-1.We also report an estimate of the rate constant for the reaction I+K2-> KI+K of k3(T=567 K)= ca. 5x10-10 cm3 molecule-1 s-1, in accord with the reaction cross section reported for the analogous reaction of Br+K2 derived from molecular beams.The recombination reaction has been modeled by trajectory calculations over the appropiate potential surfaces, the large value of k1 being governed by the ionic surface constructed on the basis of the Rittner potential function, which crosses the covalent surface 11.3 Angstroem, and by the large impact parameters for reaction.Detailed dynamical calculations on these surfaces employing Monte Carlo techniques have been found to account both for the present measurements and for high-temperature dissociation rate data for KI derived from shock tube measurements.These calculations, coupled with the present measurements at T=567 K, indicate a low negative temperature dependence of the form k1(567 K-31T-0.13 cm6 atom-2 s-1, consistent with previous measurements and calculations on the analogous recombination between Cs+I+He and emphasizi ng the dominance of the ionic surface.

The invention relates to a process for preparing potassium and potassium compounds

A new class of fast thermal gas-phase reactions of the direct substitution of atoms in polyatomic molecules by atomic reactants is discovered. The Arrhenius parameters are determined for the reactions of atomic deuterium with a number of hydrogen-containing compounds, occurring via the direct substitution of hydrogen atoms and via the abstraction of hydrogen atoms. Fast substitution of alkali metal atoms from the crystals of their salts for the reaction chain carriers of hydrogen flames is found. The importance of reactions of these types in chain combustion is demonstrated. The kinetic isotope effects of hydrogen atom abstraction from hydrocarbon molecules by hydrogen and deuterium atoms are studied. A method for the kinetic studies of free atoms and radicals is developed, which takes into account the role of longitudinal diffusion in the jet and does not require the knowledge of the concentrations of atoms and radicals or the rate constants of other reactions.

The specific kinetic features of a class of fast gas-phase reactions of the direct displacement of atoms from valence-saturated polyatomic molecules interacting with an atomic reactant discovered by the author are considered. An EPR-based technique for studying the kinetics of reactions of free atoms and radicals is described, which makes it possible to consider the role of longitudinal diffusion under flow conditions and requires no knowledge of absolute concentrations of the atomic reactant. For a wide temperature range, the experimental rate constants for abstraction and displacement reactions between free deuterium atoms and various types of hydrogen-containing compounds and reactions of hydrogen atoms with a number of hydrocarbons are reported. The kinetic isotope effect of the heterogeneous recombination of hydrogen and deuterium atoms on quartz is studied. It is suggested that reactions of atom displacement from molecules should be considered when studying mechanisms of complex processes with the use of isotopes.

A bibliographical study of the reactions of NaK alloys with their oxides did not explain the related accidents that have occurred in the past, particularly those involving the handling of bubblers installed to remove traces of oxygen and water vapor from blanket gases of LMFR (liquid metal fast reactors). Moreover, it revealed a controversy with respect to the explosive hazard of the NaK alloys + KO2 reaction. A thermodynamic study of the reaction of a NaK alloy with oxygen as well as experimental work on mixtures containing NaK and different oxides (KO2, Na2O, Na2O2) led to the conclusion that violent reactions occurring at ambient temperature, were always linked to the presence of hydrated superoxides or hydroxides. On contact with NaK alloys, these hydrated compounds lead to the formation of hydrogen with a release of heat causing the decomposition of potassium superoxide KO2 and the simultaneous release of oxygen. The oxidation of liquid NaK alloy, by bubbling a mixture of argon and air containing traces of water vapor (H2O 2, besides the hydrated compounds Na2O2·2H2O, NaOH·H2O and KOH·H2O. The gas follows preferential paths and the product obtained is highly heterogeneous in both composition and hardness (porous parts and dense parts). Hydrated superoxide and hydroxides treated under vacuum result in nearly quantitative dehydration after heating at 100 °C. For storage elements or safety valves, containing NaK that has been submitted to slow surface oxidation and hydration, the oxidized layer contains KO2, Na2O2·nH2O and hydrated hydroxides of sodium and potassium. In order to avoid any hazard due to the contact of the oxides with the residual NaK alloy during transport or under impact, it is necessary to freeze the alloy and to reheat it very slowly. Operations such as draining should also be performed slowly, after having calibrated the tanks (temperature and pressure). Therefore the use of NaK liquid alloy to purify gases is questionable; as preferential paths are established, it remains impossible to predict the period of efficiency of a bubbler. Moreover, the NaK alloy does not chemically transform all traces of water vapor; because some remains present in the form of hydrated products, leading to the formation of wastes with a potential hazard during storage or destruction. In our opinion, this method of purification should be abandoned.

New compounds in the K-Ag, K-Ni, and K-Pd systems have been found to form upon compression of mixtures of the elements in a Mao-Bell diamond anvil cell. The formation of these compounds under pressure and the techniques developed to investigate their formation and crystal structures willbe described. Compounds formed between alkali metals and transition met als are of interest because it is possible that potassium may be incorporated into Earth's core, which is composed primarily of the transition metal iron. Furthermore, unusual crystal and electronic structures may result because of the novel chemical composition of the alkali metal-transition metal compounds and the transition to d-electorn bonding at high pressure.

Cs5[Na{W4N10}] was prepared from a mixture of NaNH2, CsNH2 and tungsten powder (molar ratio 1:10:4) at 700°C in autoclaves. After the reaction is finished the nitride is embedded in an alkali metal matrix. Dark red crystals were isolated by washing out the alkali metal with liquid ammonia at room temperature. The structure of Cs5[Na{W4N10}] was solved by X-ray single crystal data: I41 (No. 80), Z = 4, a = 13.926(3) A, c = 8.723(3) A, Z(Fo2) ≥ 3σ(Fo2) = 1535, Z(Variables) = 63, R/Rw = 0.040/0.052. The compound is highly sensitive against moisture giving oxotungstates and ammonia. It contains a framework of tetrahedra ∞3[WNN3/21.5-]. Sodium shares four terminal nitrogen ligands. Including sodium a distorted, β-cristobalite type arrangement ∞3[Na{W4N10}5-] results. It contains caesium in all interstices formed by twelve nitrogen ligands in so-called Friauf polyhedra. Johann Ambrosius Barth 1996.

The preparation and crystal structure of the novel ternary oxides M3AuO (M=Cs, Rb, K) containting anionic gold is reported. Cs3AuO (a=7.830(1) A, c=7.060(1) A) crystallizes as an hexagonal, Rb3AuO (a=5.501(1) A), K3AuO (a=5.240(1) A) as a cubic anti perovskite. Concerning to the ionic description (M(1+))3Au(1-)O(2-) in Cs3AuO gold exists as an anion. In Rb3AuO and K3AuO the anionic character of gold decreases respectively. The analysis of bond length and molar volumes gives support to this view, as well as investigations of conductivity and magnetic properties do.

The recombination reaction K + O2 + M was studied by the technique of pulsed photolysis of a K atom precursor followed by time-resolved laser induced fluorescene spectroscopy of K atoms at λ = 404 or 760 nm.Termolecular behavior was demonstrated and absolute third-order rate constants obtained over the temperature range 250-1103 K.A fit of this data to the form AT-n yields k(T,M = N2) = -30>(T/300)-(1.32+/-0.04) cm6 molecule-2 s-1 and k(T,M = He) = -30>(T/300)-(1.22+/-0.07) cm6 molecule-2 s-1.These results are compared to two previous studies of these reactions by different experimental methods, which were in marked disagreement below 600 K.A lower limit of D0(K-O2) > 203 kJ mol-1 is derived.The rate coefficients are then extrapolated from the experimental temperature range to ambient mesopheric temperatures (140 K T 240 K) and to flame temperatures (1500 K T 2200 K), by means of the Troe formalism.Finally, the rates of formation and bond energies of LiO2, NaO2, and KO2 are compared.

Reduction of bis(η6-arene)vanadium(0) complexes with potassium gives the corresponding bis(η6-arene)vanadium(-I) derivatives (arene = C6H6, 1,3,5-C6H3Me3) as their K+ salts. A single-crystal diffraction study of solvated K[(η6-1,3,5-C6H3Me3) 2V] shows that the anion presents two different rotameric configurations in the solid, though the sandwich structure is preserved, and that contact ion pairs are established with the K+ cations, which also interact with THF and dioxane solvent molecules. Crystal data: monoclinic, space group P21, a = 10.213 (2) A?, b = 18.518 (3) A?, c = 13.402 (3) A?, β = 89.58 (1)°, V = 2534.6 A?3, and Z = 4.

Shock-induced dissociation and the subsequent chemical relaxation processes of diatomic alkali halide molecules have been studied by time-resolved absorption spectrometry of alkali atoms, halide ions, and alkali halide molecules.The salts studied in detai

Kinetic data for the electroreduction of alkali metal cations in dimethylformamide and acetonitrile are reported at a variety of indium amalgam electrodes and at a gallium-indium electrode (eutectic composition).The kinetic parameters were found to depend markedly on the nature of the electrode material in which the product alkali metal is soluble.The data are discussed on the basis of a model in which adsorption of metal cation on the electrode and transfer of the cation from the solution phase to the metal phase are assumed to be the rate-controlling steps.This model provides an excellent description of the variation in the kinetic parparameters with electrode composition and potential.

Thermodynamic properties were obtained for several potassium-containing species by means of a series of effusion-mass-spectrometric studies.These included vaporization and dissociation experiments for KOH(g) correlated by both second and third laws, and resulted in a recommended standard enthalpy of formation: ΔH0f(298.15 K) = -(228.0+/-2.0) kJ*mol-1.MHD electric-power calculations have previously been based on a ΔH0f(298.15 K) of -(232.6+/-12.5) kJ*mol-1.Of major importance to MHD is the reduction of the uncertainty to +/-2 kJ*mol-1, which reduces the error limits in the computed power from up to 150 per cent to less than 25 per cent.An experimental standard entropy of (238.1+/-4.0) J*K-1*mol-1 was obtained from the second-law correlation for KOH(g).A dissociation energy of (261.9+/-4.0) kJ*mol-1 for KO(g) to K(2S1/2) and O(3P2) ground-state atoms was obtained.This study also yielded a value of (193.3+/-16.0) kJ*mol-1 for D0(KH,g) to K(2S1/2) and H ground-state atoms, the first reported thermochemical measurement.Second- and third-law calculations of the enthalpy of formation and atomization energy for K2O(g) yielded recommended values of -(155.5+/-12.0) kJ*mol-1 and (581.6+/-12.0) kJ*mol-1, respectively.

The reaction of alkali dimers with oxygen atoms has been studied in a crossed beam experiment.Strong chemiluminescence of the reaction products was observed.It is shown that the luminescence was emitted by alkali from the reaction M2+O->MO+M* (M alkali atom).M* can be excited up to exoergicity of this reaction at least in the cases M=Cs and Na.For M=Cs, detailed rate constants for the excitation of the different excited states have been determined using both laser induced fluorescence and chemiluminescence.The rates decrease nearly exponentially as a function of the excitation energy.They partly follow the expectation of statistical theories.Absolute reaction cross sections have been determined for all of the reactions investigated.They agree partially with those predicted by the harpoon model.

This invention relates to 2-substituted and 2,6-disubstituted penem compounds of the formula STR1 wherein Y is hydrogen, halo or certain organic substituents and X represents certain organic substituents. Also included in the invention are pharmaceutically acceptable salts of the above compounds and derivatives of the above compounds in which the carboxyl group at the 3-position is protected as by an easily removable ester protecting group. The compounds of the present invention are potent antibacterial agents or are of use as intermediates in the preparation of such agents.

The ternary oxides KCuO and K//4CuO//3 have been observed as products in the solid state reactions of potassium oxide with the oxides Cu//2O and CuO under argon and in vacuum. The compound K//4CuO//3 has been isolated as a single phase and its X-ray powder diffraction pattern has been obtained. Both Cu//2O and CuO are reduced by liquid potassium to copper metal, with the formation of the ternary oxides KCuO and K//4CuO//3. Thermal analysis showed that Cu//2O reacts with liquid potassium at 185 degree C and that CuO undergoes the same reaction at 70 degree C.

The results of an investigation of uranium interaction with alkali metal fluorides at 1273 K and above under nonequilibrium conditions are presented. The processes are accompanied by evaluation of alkali metal vapors and formation of uranium tetra and tri