Time-resolved study of mercury atom production and removal following the photolysis of HgBr2 at 193 nm

Atomic mercury is detected following the photolysis of HgBr₂ at 193 nm. The photodissociation yield of Hg is estimated to be 0.01 ± 0.01. Formation of Hg in the disproportionation of HgBr is slow, proceeding with a rate constant < 5 × 10^?16 cm³ molecule^?1 s^?1. Removal of Hg is dominated by inefficient heterogeneous processes.     

UV absorption cross section and fluorescence efficiency of HgBr2

The absorption cross section of HgBr₂ has been determined from 190 to 240 nm The relative efficiency for production of HgBr(B²Σ⁺) fluorescence has been measured for photodissociation of HgBr₂ at individual wavelengths over the range 190–210 nm. The absolute fluorescence efficiency of HgBr₂ excited at 193 nm has been determined to be 0.95.     

(HgBr2)3(As4S4)2: An Adduct of HgBr2 Molecules and Undistorted As4S4 Cages

(HgBr₂)₃(As₄S₄)₂ is obtained by high temperature reaction of stoichiometric amounts of HgBr₂ and As₄S₄. It crystallizes in the monoclinic space group P2₁/c with the lattice constants a = 9.593(5) Å, b = 11.395(5) Å, c = 13.402(5) Å, β = 107.27(3)°, V = 1399(1) ų, and Z = 2. The crystal structure consists of molecular units built from two undistorted As₄S₄ cages which are coordinated weakly by three almost linear HgBr₂ units. Raman spectra clearly indicate minor bonding interactions between HgBr₂ and As₄S₄.     

Darstellung und Struktur des Mercuroarsoniumbromo-bismutats [Hg7(HgBr)2As4] [Bi2Br10]

Formation and Structure of the Mercuroarsonium-bromobismuthate [Hg₇(HgBr)₂As₄][Bi₂Br₁₀] The crystal structure of the compound Hg₉As₄Bi₂Br₁₂, obtained by solid state reaction, was determined by single crystal X-ray diffraction. It consists of a polymeric cation framework [Hg₇(HgBr)₂As₄⁴⁺] formed by chaines of Hg₄As tetrahedrons, which are connected by mercury atoms. At several positions this connection is truncated by terminal HgBr groups. The bromobismuthate anion consists of two distorted octahedrons connected by a common bromine atom. One of the other bromine atoms is located so far from the central bismuth atom, that it must be correlated to a terminal HgBr group in the cationie network rather than to the anion. Thus the composition is Bi₂Br₁₀^4?.     

Interaction of components in the HgBr2-CdBr2-PbBr2 ternary system

The interaction in the HgBr₂-CdBr₂-PbBr₂ ternary system was studied by differential thermal analysis; the isoconcentration section of the system at 50 mol % CdBr₂ was investigated. Based on the results of the study, a projection of the liquidus surface of the HgBr₂-CdBr₂-PbBr₂ ternary system to the composition triangle was constructed; the boundaries of the primary crystallization fields were determined for three phases: HgBr₂ (degenerate field), solid solution α based on CdBr₂, and solid solution β based on PbBr₂; and isotherms were drawn. A ternary eutectic has the composition 93 mol % HgBr₂-1 mol % CdBr₂-6 mol % PbBr₂ and melts at 235°C.     

HgBr2-CsPbBr3 and CsHgBr3-PbBr2 joins of the HgBr2-PbBr2-CsBr system

The HgBr₂-CsPbBr₃ (1) and CsHgBr₃-PbBr₂ (2) joins of the HgBr₂-PbBr₂-CsBr system are studied using differential thermal analysis (DTA) and X-ray powder diffraction. Both joins are non-quasi-binary. The primary phase fields, joint crystallization fields, and invariant temperatures are determined along these joins. X-ray powder diffraction results validate the diagrams mapped for these joins.     

Experimente und Modellrechnungen zum chemischen Transport von WO2 mit HgCl2 oder HgBr2

Experiments and Calculations on the Chemical Transport of WO₂ with HgCl₂ or HgBr₂ Transport experiments with WO₂ or WO₂ + W₁₈O₄₉ or W + WO₂ as starting phases show that HgCl₂ or HgBr₂ are suitable transport agents. When using HgBr₂ we observed (in customary silica ampoules) unusual high transport rates n′ > 1000 mg/h. Experimental and calculated results agree to a large extent if the presence of small amounts of H₂O from the quartz glass wall and the resulting gaseous particles (for example HCl or HBr) formed under equilibrium conditions as well as an influence of convection are taken into consideration.     

Crossed molecular beam chemiluminescence study of the metastable mercury reaction: Hg(3P)+Br2 → HgBr(B) + Br

Chemiluminescence from HgBr(B) formed in the reaction of Hg(6³P_o with Br₂ has been observed using a N₂-seeded nozzle beam of metastable Hg³P_o) atoms. The cross section has been estimated to be 3⁺³_?2 at a collission energy of 0.33 eV. This value is smaller by more than an order of magnitude than the corresponding value for Hg(³P₂) atoms measured by Krause et al., in accordance with their inference based on less direct evidence.     

Zum chemischen Transport von Wolfram mit HgBr2 – Experimente und Modellrechnungen

On the Chemical Transport of Tungsten using HgBr₂ – Experiments and Thermochemical Calculations Using HgBr₂ as transport agent tungsten migrates in a temperature gradient from the region of higher temperature to the lower temperature (e.g. 1 000 → 900°C). The transport rates were measured for various transport agent concentrations (0.64 ? C(HgBr₂) ? 11.74 mg/cm³; T? = 950°C) and for various mean transport temperatures (800 ? T? ? 1 040°C). Under these conditions tungsten crystals were observed in the sink region. To observe the influence of tungsten dioxide (contamination of the tungsten powder) on the transport behaviour of tungsten, experiments with W/WO₂ as starting materials were performed. According to model calculations the following endothermic reactions are important for the migration of tungsten: In the presence of H₂O or WO₂ other equilibria play a role, too. Using a special “transport balance” we observed a delay of deposition of tungsten (e.g. T? = 800°C; 15 h delay of deposition) with W and W/WO₂ as starting materials. The heterogeneous and homogeneous equilibria will be discussed and an explanation for the non equilibrium transport behaviour of tungsten will be given.     

Interaction of components in the Cs2HgBr4-Cs2ZnBr4-CsBr ternary system

The interaction of components in the Cs₂HgBr₄-Cs₂ZnBr₄-CsBr ternary system was studied by differential thermal and X-ray powder diffraction analyses. The liquidus surface consists of the crystallization fields of three phases: CsBr, a solid solution of Cs₂HgBr₄ with Cs₂ZnBr₄ (??), and solid solution ?? based on Cs₃ZnBr₅. The ternary eutectic near Cs₂HgBr₄ has the coordinates ??83 mol % Cs₂HgBr₄, 2 mol % Cs₂ZnBr₄, and 15 mol % CsBr and the melting point ??415°C. The triangulating section Cs₂HgBr₄-Cs₃ZnBr₅ is characterized by the eutectic interaction with the eutectic that is degenerate near Cs₂HgBr₄, contains ??3 mol % Cs₃ZnBr₅, and melts at 420°C. This section divides the Cs₂HgBr₄-Cs₂ZnBr₄-CsBr ternary system into two ternary systems Cs₂HgBr₄-CsBr-Cs₃ZnBr₅ and Cs₂HgBr₄-Cs₃ZnBr₅-Cs₂ZnBr₄.     

Zum chemischen Transport von Molybdän mit HgBr2 — Experimente und Modellrechnungen

On the Chemical Transport of Molybdenum using HgBr₂ ? Experiments and Thermochemical Calculations . Mo migrates under the influence of HgBr₂ in a temperature gradient (e.g. 1 000→900°C). Besides elementary Mo we observed in some experiments the occurence of MoBr₂ and MoO₂ (from oxygen containing impurities) respectively. The transport behaviour (deposition sequence; deposition rates of various phases) has been enlightened by continous measurement of the mass change during the transport experiments using a special “transport balance”. Thus obtained deposition rates m(Mo) for molybdenum reached in the temperature region 800 ≤ T ≤ 1 040°C a maximum at T = 980°C independend from the starting material (Mo or Mo/MoO₂ mixtures). For variable densities D of transport agent at a constant temperature (T = 950°C) increasing values for m(Mo) were observed (m(Mo) = 23 mg/h, D_max = 8.61 mg HgBr₂/cm³). Thermochemical calculation give strong evidence for the migration of Mo via the endothermal reaction . The experimental deposition rates are about half as large than the calculated values. Good agreement between calculations and experiments were obtained only assuming the presense of oxygen in the starting materials.     

Reactions of Hexanuclear Niobium and Tantalum Halide Clusters with Mercury(II) Halides. I. Synthesis and structures of the semiconducting compounds [M6Br12(H2O)6][HgBr4] · 12H2O,MNb,Ta

A method for the preparation of new solvated clusters of the composition [M₆Br₁₂(H₂O)₆][HgBr₂X₂] · 12H₂O (M?Nb, Ta; X?Cl, Br, I) is given. The cubic crystals of [Nb₆Br₁₂(H₂O)₆][HgBr₄] · 12H₂O 1 and [Ta₆Br₁₂(H₂O)₆][HgBr₄] · 12H₂O 2 were characterized by the X-ray structure analysis: 1 : cubic, space group Fd3 m, a = 21.0072(6) Å, Z = 8, R = 0.051 (R_w = 0.066); 2 : cubic, space group Fd3 m, a = 20.9698(1) Å, Z = 8, R = 0.038 (R_w = 0.050). 1 and 2 contain octahedral cluster cation [M₆Br₁₂(H₂O)₆]²⁺ and tetrahedrally arranged [HgBr₄]^2? anion. The M? M bond distances are 2.949(1) Å for 1 and 2.9000(8) Å for 2 . The Hg? Br bond distances in [HgBr₄]^2? anion are 2.614(2) Å in 1 and 2.622(2) Å in 2 . The crystal packing patterns of the isostructural clusters 1 and 2 involve the three-dimensional hydrogen bond network; the crystalline water molecules act as donors of hydrogen to the bromine atoms of the cluster and [HgBr₄]^2? units, whereas the coordinated water molecules form hydrogen bonds to the crystalline water molecules. [Nb₆Br₁₂(H₂O)₆][HgBr₄] · 12H₂O is diamagnetic and semiconducting with the activation energy, E_a = 0.20 eV.     

The production of H(2S) atoms in the energy-transfer reaction of O2(1Δg) with HO2(X̃2A″)

The reaction of O₂(¹Δg) with HO₂(X?) was studied in an isothermal flow reactor in the pressure range 7?p? 10.7 mbar at temperatures between 299?T? 423 K. H-atom production was observed in the reaction O₂(¹Δg) + HO₂(òA′) - H(²S)+ 2O₂ (³Σ_g^?). The rate of this reaction (k₁) is estimated to be k₁ = (1 ± 0.5) × 10¹⁴ CM³ Mol^?1 s^?1. The implications of this reaction to recent determinations of the rate of the reaction H + O₂(¹Δg) are discussed.     

The fast reaction of CH2OH with O2

The rate coefficient of the reaction CH₂ + O₂OH → HO₂ + CH₂O, has been measured at 300 K by the LMR flow-tube method, and found to have the unexpectedly large value k = (2_?1⁺²) × 10^?12 cm³ molecule^?1 s^?1. This reaction, preceded by isomerization, may be an important route for the oxidation of CH₃O in the upper atmosphere.     

Rate coefficient for the reaction OH + HO2 = H2O + O2 at 1 atmosphere pressure and 308 K

The rate coefficient for the reaction OH + HO₂ =H₂O + O₂ has been determined from measurements of the steady-state absorption of HO₂ at 210 nm, in low-frequency square-wave modulated photolysis of O₃ + H₂O mixtures. The value obtained was (9.9 ± 2.5) × 10^?11 cm³ molecule^?1 s^?1 at 308 K and 1 atm pressure.     

FTIR study of the DMS/NO2/I2/N2 photolysis system: The reaction of IO radicals with DMS

A steady-state system involving the photolysis of NO₂ in an excess of I₂ as a source of IO radicals has been used to study the reaction IO + DMS in 760 Torr N₂ at 296 K. IO radicals were found to react rapidly with DMS, one molecule of DMSO being produced for each molecule of DMS consumed. Numerical analysis of the experimental results yielded a rate constant of (3.0 ± 1.5) × 10^?11 cm³ s^?1 for the reaction IO + DMS → DMSO + I.     

Vibrational emission of NO2 from the reaction of NO with O3

Vibrational chemiluminescence in the Δν₁ = Δν₃ = ?1 band of NO₂ is observed both in the O + NO and O₃ + NO reactions and shown to be emitted by molecules with up to 11 000 cm^?1 of vibrational energy. Quenching rate constants of NO₂³ are estimated ranging from about 6 × 10^?14 for Ar to about 3 × 10^?12 cm³ s^?1 for NO₂. The ratio of vibrational to electronic emission is 0.06 ± 0.03 for O + NO and 5.3 ± 1.0 for O₃ + NO. It is suggested that vibrationally excited NO₂ is a major product of that channel of the O₃ + NO reaction which forms ground-state NO₂(²A₁) directly.     

Electrochemical properties of the AlBr3/MBr/ArH solvent system and polarography of metal ions in it

Physical and electrochemical properties of the AlBr₃/MBr/ArH system with different metal ions added were studied. Nernst plots for the Hg/Hg²⁺ and Zn/Zn²⁺ couples were measured and the formal potentials were found to be 0.65–0.68 V (RAIE) for the former and 0.08 V (RAIE) for the latter. The slopes of the Nernst plots were 29±1 mV as expected. The exchange current density for deposition and dissolution of mercury was found to be 18.5 μA cm^?2 and 73 μA cm^?2 in 0.1 mM and 1.0 mM solutions of HgBr₂, respectively,The density of the solution was found to increase linearly with increasing concentration of AlBr₃, and its values in toluence and mesitylene were practically identical. The viscosity increased rapidly from a value of ca. 0.5–0.6 cP for the pure solvents to 1.9 cP and 4.0 cP for 2.3 M AlBr₃, 0.76 M KBr in toluence and mesitylene, respectively. The measured diffusion coefficients of Hg²⁺ were in the range of (0.8–2.0)×10^?6 cm²s^?1 in mesitylene (depending on the concentration of AlBr₃ and KBr) and 4.0×10^?6 cm²s^? in toluene. The calculated ionic radius was 6.3±1 Å in mesitylene and 2.3±0.5 Å in toluene. The diffusion coefficient for Ag⁺, ions was found to have similar values.The specific conductivity was found to increase with concentration of (KAl₂Br₇). The molar conductivity also increases with increasing concentration. When corrected for the change of viscosity, the normalized molar conductivity increases linearly with the square of the concentration of (KAl₂Br₇).A detailed survey of existing literature data for this and similar systems is presented.     

Crystal structure,phase transitions and dielectric properties of the mixed compound [Cs0.92(NH4)0.08]2HgBr4

The crystal structure of [Cs_0.92 (NH₄)_0.08]₂HgBr₄ was determined by three-dimensional X-ray diffraction analysis. The space group is Pnma with a = 10.210(2), b = 7.928(1), c = 13.883(1)Å and Z = 4 at 293K. The structure was refined to R = 0.067. The distribution of atoms can be described as isolated HgBr₄²⁻tetrahedra , Cs⁺ and NH₄⁺ cations. The main feature of this structure is the coexistence of two types of bonds: Cs⁺  Br⁻ ionic bonds and NH…Br hydrogen bonds ensuring the cohesion of the crystal. Dicaesium-ammonium tetrabromomercurate exhibits three phase transitions at T₁ = 237K, T₂ = 244K and T₃ = 513K. These transitions were detected by differential scanning calorimetry and analysed by dielectric measurements using the impedance and modulus spectroscopy techniques. The phase change at high temperature is related with the orientational disorder of NH₄⁺ cations. Transport properties in this material appear to be due to a H⁺ ion hopping mechanism.