Thiosulfatothiourea lead complexes

Interactions in the system Pb(NO₃)₂-Na₂S₂O₃-(NH₂)₂CS-H₂O were studied using UV spectroscopy. The results of the study indicate a possibility of complete substitution of thiourea for thiosulfate ions when the solution concentration is 10^?3 mol/L. The compounds PbS₂O₃ · (NH₂)₂CS · H₂O and PbS₂O₃ · 2(NH₂)₂CS · H₂O were isolated from concentrated aqueous solutions and characterized by IR spectroscopy and thermal analysis. The structure of these compounds is suggested. Thermolysis schemes for these compounds are suggested on the basis of the IR absorption spectra of thermolysis products.     

Study of photolysis of K4[Cd(S2O3)3] solutions in aqueous isopropanol

Photolysis of K₄[Cd(S₂O₃)₃] solutions in aqueous isopropanol under irradiation with high-pressure mercury-quartz lamp has been studied by spectroscopy methods. The photolysis products have been identified by X-ray diffraction analysis; their formation mechanism has been suggested. The primary photolysis product is nanosized CdS, its irradiation initiating further redox transformations of the solution components to give the final products.     

The photochemical formation of cometary radicals

The present state of our knowledge of the photochemical formation of cometary free radicals is reviewed. The evidence shows that the photodissociation of water can explain the formation of O, OH, H and H₂O⁺. Some of the other radicals such as CN and NH₂ can also be explained by the photodissociation of stable compounds such as HCN, CH₃CN and NH₃. Other radicals such as NH, C₂, and C₃ do not appear to originate from the direct photolysis of any stable parent compound. The photolysis of free radicals that are formed as primary products in the photolysis of stable parent molecules has been suggested as an alternate source for these radicals. It is shown that such a process would be consistent with the currently available laboratory data and with cometary observations.     

Carbon-13 isotope enrichment in the photolysis of CO with the 123.58 nm Kr resonance radiation

The 123.58 nm Kr resonance radiation was shown to excite selectively the ¹³CO(A ¹Π-X¹Σ⁺) 13,0 transition in natural isotopic composition CO. The photolysis products, CO₂ andC₃O₂, were enriched in carbon-13. Carbon dioxide was enriched ten-fold and the central carbon of C₃O₂ was enriched sixty-fold.     

激光诱导的亚硝酸与二苯醚的反应机理

355 nm光照下利用瞬态吸收光谱技术进行了有氧、无氧条件下二苯醚与亚硝酸体系的反应机理研究, 考察了其中瞬态物种的衰减行为, 并对其光解产物进行了GC-MS分析. 研究表明, HNO₂在355 nm紫外光的照射下产生的OH自由基和二苯醚反应生成C₁₂H₁₀O-OH 加合物, N₂条件下C₁₂H₁₀O-OH衰减的速率常数为(1.86±0.14)×10⁵ s^－1, 在有氧条件下, C₁₂H₁₀O-OH可转化为C₁₂H₁₀O-OHO₂, 衰减的速率常数为(6.6±0.4)×10⁶ s^－1. N₂条件下最终产物为苯酚、2-羟基二苯醚、4-羟基二苯醚、4-硝基二苯醚.     

UV laser photolysis of silacyclopent‐3‐ene: effect of admixtures on nature of chemically vapour‐deposited organosilicon films

Examination of ArF laser‐induced gas‐phase photolysis of silacyclopent‐3‐ene, occuring as extrusion of silylene, in the presence of admixtures reveals that photolysis is not interfered with in the presence of N₂, CO and CO₂, but it is in the presence of O₂, 2‐C₄F₈, CH₃OH, CD₃OH, CF₃CH₂OH and CH₃CO₂H. Formation of volatile products and solid deposited films incorporating fluorine or oxygen atoms is interpreted in terms of reactions of silylene with the admixtures. Copyright © 2002 John Wiley & Sons, Ltd.     

FTIR spectroscopic studies of the CH3S + NO2 reaction under atmospheric conditions

Product studies using FTIR absorption spectrometry have been performed in a 420 xxx reaction chamber on the 254 nm photolysis of mixtures containing CH₃SSCH₃ and NO₂ at ppm concentrations in 760 Torr of O₂/N₂ diluent. The results indicate that the CH₃S radicals formed by photolysis of CH₃SSCH₃ react primarily with NO₂, forming CH₃SO and NO. In the presence of O₂ an unstable intermediate whose IR absorption spectrum resembles a peroxynitrate compound is observed. The intermediate has been tentatively assigned to methyl sulfinyl peroxynitrate, CH₃S(O)OONO₂. Other products include SO₂, CH₃SNO, CH₃SNO₂, CH₃NO₃, CH₃SO₃H, and HCHO.     

N2O5 photolysis products investigated by fluorescence and optoacoustic techniques

Pulsed laser photolysis of N₂O₅ near 290 nm coupled with fluorescence detection (calibrated by NO₂ photolysis) showed that the O(³P) quantum yield is ≤0.1. A pulsed laser optoacoustic technique in a flow tube (ca. 6 torr of N₂) was tested by photolysis of NO₂ and then applied to N₂O₅. Nitric oxide was added to react with NO₃ free radical and the resulting increase in the optoacoustic signal confirmed the presence of NO₃ free radicals. Based on the relative optoacoustic signals observed for NO₂ and N₂O₅, the quantum yield for NO₃ production is 0.8 ± 0.2.     

Rate constants for the reactions of HCCCO and NCCO radicals with molecular oxygen

Reactions of HCCCO and NCCO radicals with O₂ have been studied by a combination of pulsed laser photolysis and photoionization mass spectrometry. HCCCO was produced by 193‐nm photolysis of methylpropiolate or 3‐butyn‐2‐one, and NCCO was formed by 193‐nm photolysis of acetylcyanide. The rate constants obtained at 298 ± 3 K were (6.5 ± 0.7) × 10^?12 cm³ molecule^?1 s^?1 for the HCCCO + O₂ reaction, and no pressure dependence was observed between 1.5 and 16 Torr of N₂ as a bath gas. Because HCO and HCCO radicals were observed as reaction products, it was confirmed that the reaction proceeds by a two‐body reaction. On the other hand, the rate constants of NCCO with O₂ depended on the total pressure and were (5.4–8.8) × 10^?13 cm³ molecule^?1 s^?1 for total pressures 2.0–15.5 Torr of N₂, confirming that the reaction proceeds by a three‐body process. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 440–448, 2001     

The reaction of CH3O2 radicals with NO2

The rate constant for the reaction CH₃O₂ + NO₂ → (products) has been measured directly by flash photolysis and kinetic spectroscopy. At room temperature and at total pressures between 53 and 580 Torr, k₃ = (9.2 ± 0.4) × 10⁸ liter/mole sec so that the rate of formation of the probable primary product peroxymethyl nitrate (CH₃O₂NO₂) may be significant in urban atmospheres.     

Chlorine nitrate photolysis by a new technique: very low pressure photolysis

Very low pressure photolysis (VLPØ) of chlorine nitrate was performed in a quartz Knudsen cell. The light source was a 2500 W high-pressure xenon lamp, and a modulated molecular-beam mass spectrometer was used to monitor the concentration of ClONO₂ and photolysis products. Because of the low pressures used (? 10^?3 torr) and the short residence time in the cell (≈1 s), secondary reactions were unimportant and the primary products could be directly identified. The primary photolysis products (λ ≈ 2700 Å) are atomic chlorine and NO₃ free radical. Chlorine atoms were identified both by the appearance of Cl₂ (wall recombination product; the walls were not poisoned) and by HCl produced when C₂H₆ was added to the cell. Nitrate free radical was directly identified as a mass peak at m/e = 62, as well as by chemical titration with nitric oxide: NO₃ + NO → 2NO₂. It was verified by direct tests that the peak at m/e = 62 did not arise from possible HNO₃ contamination or from N₂O₅, a possible secondary product. This titration reaction was used to measure quantitatively a lower limit to the primary quantum yield, φ ? 0.5 ± 0.3. This represents a lower limit because of the unknown extent of the secondary photolysis of NO₃ under our conditions. We believe this to be the first observation using mass spectrometry of the NO₃ free radical. The quantum yield for atomic chlorine is φ = 1.0 ± 0.2. N₂O was used to test for O(¹D) according to the reaction, O(¹D) + N₂O → products; none was observed. Triplet oxygen, O(³P) was observed to the extent of ≈ 10% by the reaction O(³P) + NO₂ → NO + O₂, but this yield can also be due to the photolysis of NO₃ free radical produced in the primary step. We conclude that the predominant reaction pathway is

.     

Photochemistry of iron pentacarbonyl adsorbed on titanium dioxide

The photolysis of iron carbonyl (Fe(CO)₅) adsorbed on titanium dioxide (TiO₂, anatase) was studied by FT-IR spectroscopy. When adsorbed Fe(CO)₅ is illuminated by visible and near-UV light, the IR spectrum of its photolysis products is hardly observed, indicating that most of the Fe(CO)₅ is photodecomposed to iron(0) or iron oxides on TiO₂. The carbon monoxide (CO) evolution rate upon illumination depends on the wavelength of light; 433 nm light is more effective for CO evolution than 366 nm light. This result implies that the band-gap excitation of TiO₂ has little effect on the photolysis of adsorbed Fe(CO)₅, since the absorption edge of TiO₂ (anatase) lies at around 400 nm. The effects of substrates on the photolysis of adsorbed Fe(CO)₅ are discussed with reference to previous results obtained for aluminium oxide (Al₂O₃) and silicon dioxide (SiO₂), on which the photolysis leads to the formation of Fe₂(CO)₉ or Fe₃(CO)₁₂.     

Rate coefficient for the reaction of CCl3 radicals with ozone

The rate coefficient for the reaction of CCl₃ radicals with ozone has been measured at 303 ± 2 K. The CCl₃ radicals were generated by the pulsed laser photolysis of carbon tetrachloride at 193 nm. The time profile of CCl₃ concentration was monitored with a photoionization mass spectrometer. Addition of the O₃–O₂ mixture to this system caused a decay of the CCl₃ concentration because of the reactions of CCl₃ + O₃ → products (5) and CCl₃ + O₂ → products (4). The decay of signals from the CCl₃ radical was measured in the presence and absence of ozone. In the absence of ozone, the O₃–O₂ mixture was passed through a heated quartz tube to convert the ozone to molecular oxygen. Since the rate coefficient for the reaction of CCl₃ + O₂ could be determined separately, the absolute rate coefficient for reaction ( 5 ) was obtained from the competition among these reactions. The rate coefficient determined for reaction ( 5 ) was (8.6 ± 0.5) × 10^?13 cm³ molecule^?1 s^?1 and was also found to be independent of the total pressure (253–880 Pa of N₂). This result shows that the reaction of CCl₃ with O₃ cannot compete with its reaction with O₂ in the ozone layer. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 310–316, 2003     

The rate of the reactions of C2O radicals with H and H2

The rate constants for the reactions C₂O + H → products (1) and C₂O + H₂ → products (2) have been determined at room temperature by means of laser-induced fluorescence detection of C₂O radicals, generated either by the KrF excimer laser photolysis Of C₃O₂, or by the reaction of C₃O₂ with O atoms. Values of k₁ = (3.7 ± 1.0) × 10^?11 cm³ s^?1 and k₂ = (7 ± 3) × 10^?13 cm³ s^?1 were obtained.     

Crystal Structure of the RE2PbS4 (RE = Y,Dy, Ho,Er, and Tm) Compounds and a Comparison with the Crystal Structures of other Rare Earth Lead Chalcogenides

The crystal structure of the RE₂PbS₄ (RE = Y, Dy, Ho, Er and Tm) compounds (space group Cmc2₁, Pearson symbol oC112, a = 0.79301(3) nm, b = 2.86966(9) nm, c = 1.20511(5) nm, R_Bragg = 0.0979 for Y₂PbS₄; a = 0.79484(8) nm, b = 2.8721(3) nm, c = 1.2039(1) nm, for Dy₂PbS₄; a = 0.79081(2) nm, b = 2.86222(7) nm, c = 1.20220(4) nm, R_Bragg = 0.0859 for Ho₂PbS₄; a = 0.7863(2) nm, b = 2.8525(5) nm, c = 1.1995(2) nm, R1 = 0.0482 for Er₂PbS₄ and a = 0.78419(3) nm, b = 2.84184(9) nm, c = 1.19655(4) nm, R_Bragg = 0.0893 for Tm₂PbS₄) was investigated by means of X‐ray single crystal and powder diffraction. Each RE atoms is octahedrally coordinated by six S atoms. Each Pb atoms is surrounded by seven S atoms to form a mono‐capped trigonal prism.     

Direct observation of spin-forbidden formation of O(D) in the near-UV photolysis of ozone

Time-of-flight measurements have been made of the O(¹D) fragment following the photolysis of ozone in the near-UV. At 321.9 nm fragments are seen with kinetic energies the values of which are those expected from spin-forbidden dissociation with ground state O₂(X³Σ_g⁻) molecules as the co-product. Spin-allowed dissociation of internally excited ozone molecules is also seen to produce translationally cold O(¹D) and O₂(a¹Δ_g) products. The implications for the dissociation of tropospheric ozone are briefly discussed.     

Reactions of hydroxyl radicals with polystyrene

The reaction of polystyrene with hydroxyl radicals, generated by the photolysis (λ > 300 nm) of H₂O₂, has been studied at 25° in dichloromethane solution, both under vacuum conditions and in presence of O₂. Spectroscopic analyses suggest the presence of phenols and hydroxymucondialdehydes (when O₂ is present) among the reaction products, indicating that OH addition occurs at the phenyl groups of the polymer. By comparison with initiated oxidation reactions under the same conditions, it is concluded that the OH radicals undergo mainly addition reactions. A mechanism has been produced to account for the products. The significance of OH addition reactions in the oxidation of polystyrene is considered, the OH radicals being produced by hydroperoxide decomposition during oxidation, and the products having been previously identified as containing mucondialdehydes.     

UV absorption spectra of HO2 and CH3O2 radicals and the kinetics of their mutual reactions at 298 K

We report results of a flash photolysis study of the UV, spectra of HO₂ and CH₃O₂ radicals, obtained by using a calibration technique based on the reaction Cl+NO→NOCl. We also report preliminary results from our study of the kinetics of the reaction CH₃O₂+HO₂→products at room temperature and near atmospheric pressure. Our results are consistent with the only previous direct determination of the rate constant of the second reaction: k₁ = (6.4 ± 1.0) × 10⁻¹²cm₃ molecule⁻ s⁻¹. From the same study we derive rate constants for the self-reaction of HO₂ and CH₃O₂ radicals, which agree with recommended values.     

Infrared Laser Photochemistry of Trichlorosilane

IR multiphoton dissociation of trichlorosilane molecules in scavenger gas (O₂, CO₂, OCS, halomethanes, BCl₃, TiCl₄, etc.) media was studied. Stable, volatile dissociation products were determined. It was shown that the product formation mechanism depends on the partial pressure of SiHCl₃. At a high pressure (400–800 Pa) of SiHCl₃, its photolysis in a mixture with fluorine-, chlorine-, or bromine-containing scavengers led to the formation of products of the SiF_{4 – n} Cl _n and SiBr_{4 – n} Cl _n type, where n = 1–4. An SiHCl₃ conversion into SiCl₄ higher than 70% could be achieved. The formation mechanism was proposed for the photolysis products. At a low SiHCl₃ pressure (<70 Pa), the formation of a stable volatile product was observed only in a mixture with BCl₃, which resulted from the reaction of insertion of SiCl₂ in the B–Cl bond.     

Kinetics and mechanisms of the reaction of OH radicals with dimethyl sulfide

The rate constant of the reaction of OH with DMS has been measured relative to OH + ethene in a 420 l reaction chamber at 760 torr total pressure and 298 ± 3 K in N₂ + O₂ buffer gas using the 254 nm photolysis of H₂O₂ as the OH source. In agreement with a recent absolute rate determination of the reaction the measured effective rate constant was found to increase with increasing partial pressure of O₂ in the system, for 760 torr air a rate constant of (8.0 ± 0.5) × 10^?12 cm³ s^?1 was obtained. Product studies have been performed on the reaction in air using FTIR absorption spectrometry for detection of reactants and products. On a molar basis, SO₂ was formed with a yield of 70% and dimethyl sulfone (CH₃SO₂CH₃) with a yield of approximately 20%. These results are considerably different to those obtained in other product studies which were carried out in the presence of NO_x. These differences are compared and their relevance for the atmospheric oxidation mechanisms of DMS is discussed.