Mass spectrometric in-situ determination of NO2 in gas mixtures by resonance enhanced multiphoton ionisation

One- and two-colour photoionisation spectra for NO₂ have been investigated using a time of flight mass spectrometer as detector to find the most efficient REMPI process for analytical applications. Two different inlet systems have been employed: a pulsed supersonic jet expansion stage and a flow reactor. Selective and sensitive mass spectrometric determinations of free NO₂ have been possible even in the presence of high concentrations of organic nitrates, HNO₃ and other NO₂ precursors. Employing two-colour (1+1+1) excitation using a concentration of HNO₃5·10¹⁴ molecules/cm³ a detection limit of 5·10¹¹ molecules/cm³ has been found for NO₂ whereas in the absence of HNO₃ a detection limit of 5·10¹⁰ molecules/cm³ is reported.     

An ftir study of the reaction between nitrogen dioxide and alcohols

The reaction 2NO₂ + ROH = RONO + HNO₃ (R = CH₃ or C₂H₅) has been studied using the FTIR method at reactant pressures from 0.1 to 1.0 torr at 25°C. The termolecular rate constant for the forward reaction was determined to be (5.7 ± 0.6) × 10^?37 cm⁶/molec²·s for CH₃OH and (5.7 ± 0.8) × 10^?37 cm⁶/molec²·s for C₂H₅OH, that is, d[RONO]/dt = k[NO₂]²[ROH]. The corresponding equilibrium constants were measured as 1.36 ± 0.06 and 0.550 ± 0.025 torr^?1, respectively. These results are consistent with those of a previous study based on the NO₂ decay measurements at reactant pressures from 1 to 10 torr.     

Thermische Zerfallsreaktionen von Nitroverbindungen I: Dissoziation von Nitromethan

The thermal decomposition of CH₃NO₂ highly diluted in Ar has been studied in shock waves at 900 < T < 1500 K and 1.5 · 10^?5 < [Ar] < 3.5 · 10^?4 mol/cm³. Concentration profiles of CH₃NO₂ and NO₂ were recorded. The unimolecular reaction was found to be in its fall-off range. Limiting low pressure rate constants of k₀ = [Ar] · 10^17.1 exp(?42(kcal/mol)/RT) cm³/ mol sec in the range 900 < T < 1400 K and limiting high pressure rate constants of k_∞ = 10^16.25 exp (?(58.5 ± 0.5 kcal/mol)/RT) sec^?1 have been derived. A rate constant of 1.3 · 10¹³ cm³/mol sec was found for the first subsequent reaction CH₃+NO₂ → CH₃O+NO.     

Darstellung und Charakterisierung von Phthalocyanin-π-Kation-Radikalen von H+, Mg2+ und Cu2+

Preparation und Characterization of Phthalocyanine-π-Cation-Radicals of H⁺, Mg²⁺, and Cu²⁺ The preparation of phthalocyanine-π-cation-radicals (Pc(?1)) of H⁺, Mg²⁺, Cu²⁺ is described. MgClPc(?1) and Cu(NO₃)Pc(?1) · HNO₃ are isolated as stoichiometrically pure, stable redbrown solids. Contrary to the phthalocyanines(?2) (Pc(?2)) these are very soluble with redviolet colour in organic solvents in the presence of R? COOH (R ? H, CF₃, CCl₃). The electronic absorption absorption spectra (UV-VIS) are remarkably solvent-dependent. This solvent effect is due to a reversible radical association. Monomeric radical species exist in nonpolar (CH₂Cl₂), dimeric in polar solvents (CH₃NO₂, C₂H₅OH). The UV-VIS, infrared (IR), and resonance-raman (RR) spectra of MgClPc(?1) and Cu(NO₃)Pc(?1) · HNO₃ are discussed and compared with the analogoues spectra of MgPc(?2) · 2 H₂O and MgPc(?2) · HCl. Although there are only minor differences in the chemical composition and the electronic structure the spectroscopic data vary significantly for every complex. Especially the IR spectrum is suitable for a quick demonstration of the π-cation-radicals. The diagnostic bands are at ca. 1350 and 1450 cm^?1.     

Reactivity of Semivolatile Organic Compounds with Hydroxyl Radicals,Nitrate Radicals,and Ozone in Indoor Air

Indoor semivolatile organic compounds (SVOCs) originate from indoor and outdoor sources. These SVOCs partition among different phases and available surfaces, which increases their residence time indoors to several years. SVOCs may also react with indoor oxidants, such as hydroxyl radicals (OH), nitrate radicals (NO₃), and ozone. In the present study, the second‐order reaction rate constants of 72 SVOCs in indoor air (gas and particle phases) at room temperature and ambient air pressure were retrieved from the literature. The pseudo–first‐order reaction rate constants of these SVOCs were calculated for the indoor concentration ranges of OH, NO₃, and ozone. Then, the extent to which the chemical reaction had a meaningful impact on the removal of SVOCs from the indoor environment was quantitatively analyzed. The orders of magnitude of the second‐order rate constant ranged between 10⁻¹⁵ and 10⁻¹⁰ cm³/(molecule·s) for OH/SVOC reactions, 10⁻¹⁷ and 10⁻¹² cm³/(molecule·s) for NO₃/SVOC reactions, and 10⁻²⁰ and 10⁻¹⁶ cm³/(molecule·s) for ozone/SVOC reactions in indoor air. Assuming that the highest indoor reactant concentrations were 1.8 × 10⁶ molecules/cm³ (7.3 × 10⁻⁵ ppb) for OH, 2.5 × 10⁸ molecules/cm³ (10⁻² ppb) for NO₃, and 1.4 × 10¹² molecules/cm³ (58 ppb) for ozone, the highest pseudo–first‐order rate constants in the gas phase for the studied reactions of OH/SVOCs (n = 72), NO₃/SVOCs (n = 3), and ozone/SVOCs (n = 14) reached 1.5 h⁻¹ (OH/benzo[a]pyrene), 0.41 h⁻¹ (NO₃/acenaphthene), and 1.0 h⁻¹ (ozone/aldrin and ozone/heptachlor), respectively. The pseudo–first‐order rate constants in the particle phase for the studied reactions of OH/SVOCs (n = 13), NO₃/SVOCs (n = 6), and ozone/SVOCs (n = 14) at the high indoor reactant concentrations reached 0.09 h⁻¹ (OH/DEHP), 5.8 h⁻¹ (NO₃/pyrene), and 11 h⁻¹ (ozone/benzo[a ]pyrene), respectively. These results indicate that the chemical reactions of some SVOCs in indoor air have a meaningful impact compared to the air exchange rate, which should be considered in future studies on indoor air quality modeling.     

Temperature-dependent rate constant for the reaction of F atoms with HNO3

The kinetics of the reaction of F atom with HNO₃, source of NO₃ radicals widely used in laboratory studies, has been investigated at nearly 2.7 mbar total pressure of helium over a wide temperature range, T = 220-700 K, using a low-pressure discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer. The rate constant of the reaction F + HNO₃ → NO₃ + HF (1) was determined using both relative rate method and absolute measurements under pseudo–first-order conditions, monitoring the kinetics of F-atom consumption in excess of HNO₃, k₁ = (8.2 ± 0.4) × 10⁻¹² exp((315 ± 15)/T) cm³ molecule⁻¹ s⁻¹ (where the uncertainties represent precision at the 2σ level, the estimated total uncertainty on k₁ being 15% at all temperatures). The reaction rate constant was found to be in excellent agreement with the only previous temperature-dependent study. Experiments on detection of the reaction product, HF, have shown that NO₃ and HF forming channel of the title reaction is the dominant, if not unique, on the whole temperature range of the study.     

Aktivierungsanalytische Bestimmung von Nickel in Ionenaustauschern

A method for the determination of nickel in ion exchange resins has been elaborated. It is based on the⁵⁸Ni(n, p)⁵⁸Co reaction. Samples of 500 mg are irradiated for 90 h in a fission neutron flux of 10¹³ n·cm⁻²·s⁻¹. After decomposing by HNO₃/HClO₄ mixture the radiochemical separation is carried out by extraction of the Co-DDTC-complex in chloroform. Measuring by a 23 cm³ Ge(Li) detector for 15 h provides a detection limit of 10 ppb. Radiochemical yield is determined by⁵⁷Co as radioactive indicator. Limitations by⁶⁰Co are reduced by Cd-screened activation and by anticoincidence measuring technique.      

Rate constants for: OH + NO2 (+ N2) → HNO3 (+ N2) between 220 and 358 K

Rate constants have been determined for the reaction OH + NO₂ (+ N₂) → HNO₃ (+ N₂), using time-resolved resonance absorption to follow the removal of OH radicals produced by flash photolysis of HNO₃. The measurements cover the ranges: 220 ? T ? 358 K and 3.2 × 10¹⁷ ? [N₂] ? 4.0 × 10¹⁸ molecule cm^?3.     

Ozone reduction at Nafion modified Au electrode and the measurement of ozone concentration in highly resistive solutions

The mass transport and charge transfer kinetics of ozone reduction at Nafion coated Au electrodes were studied in 0.5 mol/L H2SO4 and highly resistive solutions such as distilled water and tap water. The diffusion coefficient and partition coefficient of ozone in Nafion coating are 1.78×10-6 cm2·s-1 and 2.75 at 25℃ (based on dry state thickness), respectively. The heterogeneous rate constants and Tafel slopes for ozone reduction at bare Au are 4.1×10-6 cm·s-1, 1.0×10-6 cm·s-1 and 181 mV, 207 mV in 0.5 mol/L H2SO4 and distilled water respectively and the corresponding values for Nafion coated Au are 5.5×10-6 cm·s-1, 1.1×10-6 cm·s-1 and 182 mV, 168 mV respectively. The Au microelectrode with 3 μm Nafion coating shows good linearity over the range 0-10 mmol/L ozone in distilled water with sensitivity 61 μA·ppm-1 ·cm-2, detection limit 10 ppb and 95% response time below 5 s at 25℃. The temperature coefficient in range of 11-30℃ is 1.3%.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine : L'extraction del'acide nitrique par quelques dioxydes de diphosphine

The distribution of nitric acid between an aqueous phase of constant or variable ionic strength and a benzene solution of diphosphine dioxide can be explained by the following reactions H⁺_a+ NO_3^-a+ DiPO₀ ? D1PO·HNO₃₀ H⁺_a+ NO_3^-a+ DiPO·HNO₃₀ ? DiPO·2 HNO₃₀ At constant ionic strength, the stability constants K₁″ were determined for the complexes 1,1-DiPO·HNO₃ (98 ± 01 (M)^-1), 1,4-DiPO·HNO₃(44±3 (M)_-1) and 1,5-DiPO·HNO₃ (51 ± 1 (M)^-1). The constants K₁₁″ for the complexes 1,1-DiPO·2 HNO₃ and 1,5-DiPO.2 HNO₃ are respectively 035±001 (M)^-1 and 62 ±0.05 (M)^-1 at 25°. With an aqueous phase of variable ionic strength, values of K₁'=54±7 (M)^-2 for 1,5-D1PO.HNO₃ and K_II'=65 ± 04 (M)^-2 for 1,5-DiPO·2 HN0₃ were obtained     

Study of the kinetics of the reactions of NO3 with HO2 and OH

The Absolute rate constants for the gas-phase reactions of NO₃ with HO₂ and OH have been determined using the discharge flow laser magnetic resonance method (DF-LMR). Since OH was found to be produced in the reaction of HO₂ with NO₃, C₂F₃Cl was used to scavenge it. The overall rate constant, k₁, for the reaction, HO₂ + NO₃ → products, was measured to be k₁=(3.0 ± 0.7)×10^?12 cm³ molecule^?1 s^?1 at (297 ± 2) K and P=(1.4 – 1.9) torr. This result is in reasonable agreement with the previous studies. Direct detection of HO₂ and OH radicals and the use of three sources of NO₃ enabled us to confirm the existence of the channel producing OH:HO₂+NO₃→OH+NO₂+O₂ (1a); the other possible channel is HO₂+NO₃→HNO₃+O₂ (1b). From our measurements and the computer simulations, the branching ratio, k_1a/(k_1a + k_1b), was estimated to be (1.0). The rate coefficient for the reaction of OH with NO₃ was determined to be (2.1 ± 1.0) × 10^?11 cm³ molecule^?1 s^?1. © 1993 John Wiley & Sons, Inc.     

EPR kinetic study of the reactions of CF3Br with H atoms and OH radicals

Reactions of CF₃Br with H atoms and OH radicals have been studied at room temperature at 1–2 torr pressures in a discharge flow reactor coupled to an EPR spectrometer. The rate constant of the reaction H + CF₃Br → CF₃ + HBr (1) was found to be k₁ = (3.27 ± 0.34) × 10^?14 cm³/molec·sec. For the reaction of OH with CF₃Br (8) an upper limit of 1 × 10^?15 cm³/molec·sec was determined for k₈. When H atoms were in excess compared to NO₂, used to produce OH radicals, a noticeable reactivity of OH was observed as a result of the reaction OH + HBr → H₂O + Br, HBr being produced from reaction (1).     

A kinetic study of the decomposition of HNO3 and its reaction with NO

The rate of reaction between NO and HNO₃ and the rate of thermal decomposition of HNO₃ have been measured by FTIR spectroscopy. The measurements were made in a teflon lined batch reactor having a surface to volume ratio of 14 m^?1. During the experiments, with initial HNO₃ concentrations between 2 and 12 ppm and NO concentrations between 2 and 30 ppm, a reactant stoichiometry of unity and a first order NO and HNO₃ dependence were confirmed. The observed rate constant for the reaction at 22°C and atmospheric pressure was determined to 1.1 (±0.3) 10^?5 ppm^?1 min^?1. At atmospheric pressure, HNO₃ decomposes into NO₂ and other products with a first order HNO₃ dependence and with a rate constant of 2.0 (±0.2) 10^?3 min^?1. The apparent activation energy for the decomposition is 13 (±4) kJ mol^?1.     

Kinetics of particle growth VII. NH4NO3from the NH3-O3 reaction in the presence of air and water vapor

Our earlier work on the formation of particulate NH₄NO₃ in the NH₃? O₃ reaction at 25°C is extended to include air as a diluent and H₂O vapor as an additive. More extensive data at different values of [NH₃]/[O₃]₀ were obtained also, where [O₃]₀ is the initial O₃ concentration. In our earlier work we concluded that NH₄NO₃ vapor was dissociated to NH₃ + HNO₃ and that the HNO₃ was removed by diffusion to the walls with a rate coefficient k_diff = 0.4 min^?1 or by condensation on the suspended particles. Particles were nucleated by 8 NH₃? HNO₃ pairs when their concentration product reached 5.8 × 10²⁷ molec²/cm⁶ with a rate coefficient k_nucl of 6.2 × 10^?224 cm⁴⁵/min and removed by coagulation with a rate coefficient k_coag of 1.3 × 10^?7 cm³/min. A corrected calculation modifies the number of pairs required to 6–7 with a correspondingly changed value of k_nucl. With the more extensive data of the present study the indications are that the vapor-phase NH₄NO₃ monomer is not dissociated and that its diffusion constant for loss to the walls varies between 0.3 and 0.9 min^?1 for different reaction conditions. Nucleation occurs when the NH₄NO₃ vapor concentration reaches 1.0 × 10¹² molec/cm³ via. where r is 9 and the nucleation rate coefficient k_nucl is 3 × 10^?108 cm²⁴/min. With 5.0 or 9.5 torr of H₂O vapor present, there is an excess of particles produced over that expected from this rate coefficient, indicating an additional nucleation step in which H₂O vapor participates directly to produce a hydrated salt. The coagulation coefficient of (1.87 ± 0.14) × 10^?7 cm³/min found here is in good agreement with that found previously.     

Thermische Zerfallsreaktionen von Nitroverbindungen in Stosswellen. II: Dissoziation von Nitroäthan

A shock wave study of the thermal decomposition of nitroethane in excess Ar at temperatures 900 < T < 1350 K and total concentrations of 4,5 · 10^?6 < [Ar] < 3 · 10^?4 mol cm^?3 showed that the C? N-bond fission is the primary reaction step. This unimolecular reaction could be observed in its transition region near the high pressure limit. The derived rate constants are k_∞ = 10^15.9 exp (–57 kcal mol^?1/RT) s^?1 for the high pressure and k₀/[Ar] = 10^18.0 exp (-36 kcal mol^?1/RT) cm³ mol^?1 s^?1 (at T ? 1100–1200 K) for the low pressure limit. The observed concentration profiles of C₂H₅NO₂ and NO₂ permitted to conclude on the subsequent decomposition of the ethyl radical This reaction was found to be in the fall-off range under the applied conditions.     

Rate Coefficients of the Reactions of CN and NCO with O2 and NO2 at 296 K

The rate coefficients of the reactions of CN and NCO radicals with O₂ and NO₂ at 296 K: (1) CN + O₂ → products; (2) CN + NO₂ → products; (3) NCO + O₂ → products and (4) NCO + NO₂ → products have been measured with the laser photolysis-laser induced fluorescence technique. We obtained k₁ = (2.1 ± 0.3) × 10^?11 and k₂ = (7.2 ± 1.0) × 10^?11 cm³ molecule^?t s^?1 which agree well with published results. As no reaction was observed between NCO and O₂ at 297 K, an upper limit of k₃ < 4 × 10^?17 cm³ molecule^?1 S^?1 was estimated. The reaction of NCO with NO₂ has not been investigated previously. We measured k₄ = (2.2 ± 0.3) × 10^?11 cm³ molecule^?1 s^?1 at 296 K.     

Chemical and electrochemical behavior of metallic technetium in acidic media

The chemical and electrochemical properties of technetium metal were studied in 1–6 M HX and in 1 M NaX (pH 1 and 2.5), X = Cl, NO₃. The chemical dissolution rates of Tc metal were higher in HNO₃ than in HCl (i.e. 8.63 × 10^?5 mol cm^?2 h^?1 in 6 M HNO₃ versus 2.05 × 10^?9 mol cm^?2 h^?1 in 6 M HCl). The electrochemical dissolution rates in HNO₃ and HCl were similar and mainly depended on the electrochemical potential and the acid concentration. The optimum dissolution of Tc metal was obtained in 1 M HNO₃ at 1 V/AgAgCl (1.70 × 10^?3 mol cm^?2 h^?1). The dissolution potentials of Tc metal in nitric acid were in the range of 0.596–0.832 V/AgAgCl. Comparison of Tc behavior with Mo and Ru indicated that in HNO₃, the dissolution rate followed the order: Mo > Tc > Ru, and for dissolution potential the order: E _diss(Ru) > E _diss(Tc) > E _diss(Mo). The corrosion products of Tc metal were analyzed in HCl solution by UV–Visible spectroscopy and showed the presence of TcO₄ ^?. The surface of the electrode was characterized by microscopic techniques; it indicated that Tc metal preferentially corroded at the scratches formed during the polishing and no oxide layer was observed.     

Detection of uranium in industrial and mines samples by microwave plasma torch mass spectrometry

Microwave plasma torch (MPT), traditionally used as the light source for atomic emission spectrophotometry, has been employed as the ambient ionization source for sensitive detection of uranium in various ground water samples with widely available ion trap mass spectrometer. In the full‐scan mass spectra obtained in the negative ion detection mode, uranium signal was featured by the uranyl nitrate complexes (e.g. [UO₂(NO₃)₃]^?), which yielded characteristic fragments in the tandem mass spectrometry experiments, allowing confident detection of trace uranium in water samples without sample pretreatment. Under the optimal experimental conditions, the calibration curves were linearly responded within the concentration levels ranged in 10–1000 µg·l^?1, with the limit of detection (LOD) of 31.03 ng·l^?1. The relative standard deviations (RSD) values were 2.1–5.8% for the given samples at 100 µg·l^?1. The newly established method has been applied to direct detection of uranium in practical mine water samples, providing reasonable recoveries 90.94–112.36% for all the samples tested. The analysis of a single sample was completed within 30 s, showing a promising potential of the method for sensitive detection of trace uranium with improved throughput. Copyright © 2016 John Wiley & Sons, Ltd.     

The kinetics of chemical reactions in the products of dissociation of the CO2−H2 gas mixture in microwave discharge

The yields of hydrogen atoms, oxygen atoms and molecules, and hydroxyl radicals after a microwave discharge in the mixture of CO₂ and H₂ were measured by ESR spectroscopy in a flow-type system. A mathematical model of the kinetics of chemical reactions downstream the microwave discharge was devised. The concentrations of particles that cannot be detected under our experimental conditions were estimated. Experimental values of the concentration sensitivity for an RE-1306 ESR spectrometer are as follows: for a pressure of 1 Torr and optimized detection conditions, H^., 10¹¹ cm⁻³; O^., 3·10¹⁰ cm⁻³; OH^., 10¹⁰ cm⁻³; O₂, 3·10¹³ cm⁻³ (Ref. 7); for a pressure of 2 Torr, H^., 5·10¹² cm⁻³; O^., 2·10¹² cm⁻³; OH^., 2.5·10¹¹ cm⁻³; O₂, 7.5·10¹⁴ cm^{−3 8} Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 665–669, April, 2000.     

Room temperature rate coefficient for the reaction between CH3O2 and NO3

The molecular modulation spectroscopic technique was employed to study the kinetics of NO₃ radicals produced in the 253.7 nm photolysis of flowing gas mixtures of HNO₃/CH₄/O₂ at room temperature. By computer fitting of the NO₃ temporal behavior, a rate coefficient of (2.3 ± 0.7) × 10^?12 cm³ molecule^?1 s^?1 was obtained for the reaction between NO₃ and CH₃O₂ at 298 K.