Study of the thermal decomposition of MSO4 (M = Zn(II), Cd(II), Hg(II)) in a sodium nitrate—potassium nitrate melt

MSO₄ (M = Zn²⁺, Cd²⁺, Hg²⁺) dissolves in the molten NaNO₃—KNO₃ eutectic and is decomposed on further heating. The kinetics of decomposition have been studied at different temperatures. The decomposition of CdSO₄ and HgSO₄ in the eutectic melt obey first-order kinetics whereas the decomposition of ZnSO₄ at 420–460°C obeys second-order kinetics. However, at 480°C the decomposition of ZnSO₄ obeys first-order kinetics. The mechanism of decomposition has been given as M²⁺ +SO^2?₄ +Na⁺ +K⁺ +2NO^?₃ ? (Na,K)SO₄ + M²⁺ +2NO^?₃ M²⁺ +NO^?₃ → MO+NO⁺₂ NO^?₃ +NO⁺₂ → NO₂ + $\text{1}\text{2}$O₂ Some of the end products have been analysed by X-ray diffraction.     

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.     

A Nickel(II) Nitrite Based Molecular Perovskite Ferroelectric

The X‐site ion in organic–inorganic hybrid ABX₃ perovskites (OHPs) varies from halide ion to bridging linkers like HCOO^?, N₃^?, NO₂^?, and CN^?. However, no nitrite‐based OHP ferroelectrics have been reported so far. Now, based on non‐ferroelectric [(CH₃)₄N][Ni(NO₂)₃], through the combined methodologies of quasi‐spherical shape, hydrogen bonding functionality, and H/F substitution, we have successfully synthesized an OHP ferroelectric, [FMeTP][Ni(NO₂)₃] (FMeTP=N‐fluoromethyl tropine). As an unprecedented nitrite‐based OHP ferroelectric, the well‐designed [FMeTP][Ni(NO₂)₃] undergoes the ferroelectric phase transition at 400 K with an Aizu notation of 6/mmmFm, showing multiaxial ferroelectric characteristics. This work is a great step towards not only enriching the molecular ferroelectric families but also accelerating the potential practical applications.     

Kinetic study of the gas‐phase photolysis and OH radical reaction of E,Z‐ and E,E‐2,4‐Hexadienedial

Unsaturated 1,6‐dicarbonyls like 2,4‐hexadienedial are ring opening products in the OH initiated photo‐oxidation of aromatic hydrocarbons. In the present study, the photolysis of E,Z‐ and E,E‐2,4‐hexadienedial has been investigated under natural sunlight conditions in a large volume outdoor reaction chamber. In the case of the E,Z‐isomer, an extremely rapid isomerization into the E,E‐form was observed. The photoisomerization frequency, relative to that of NO₂, was found to be J(E,Z‐2,4‐hexadienedial)/J(NO₂) = (0.148 ± 0.012). A more complex photolysis behavior was observed for E,E‐2,4‐hexadienedial. Here, a fast equilibrium preceded a comparably slow photolysis. For the equilibrium reaction, relative frequencies of J(E,E‐2,4‐hexadienedial → EQUI)/J(NO₂) = (0.113 ± 0.009) and J(EQUI → E,E‐2,4‐hexadienedial)/J(NO₂) = (0.192 ± 0.016) were obtained, giving an equilibrium constant of K = (0.59 ± 0.07). For the photolysis frequencies, ratios of J(E,E‐2,4‐hexadienedial → products)/J(NO₂) = J(EQUI → products)/J(NO₂) = (1.22 ± 0.45)·10⁻² were determined. Qualitative aerosol measurements during the experiments showed that the photolysis of 2,4‐hexadienedials is a source of secondary organic aerosol. In addition to the photolysis study, OH radical reaction rate constants were determined, values of (7.4 ± 1.9)·10⁻¹¹ and (7.6 ± 0.8)·10⁻¹¹ cm³ s⁻¹ were obtained for E,Z‐ and E,E‐2,4‐hexadienedial, respectively. The results indicate that the dominant fate of E,Z‐2,4‐hexadienedial in the atmosphere will be photoisomerization, while for E,E‐2,4‐hexadienedial, both photolysis and OH radical reaction will be important sinks. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 689–697, 1999     

Solid‐State Interconversions: Unique 100 % Reversible Transformations between the Ground and Metastable States in Single‐Crystals of a Series of Nickel(II) Nitro Complexes

The solid‐state, low‐temperature linkage isomerism in a series of five square planar group 10 phosphino nitro complexes have been investigated by a combination of photocrystallographic experiments, Raman spectroscopy and computer modelling. The factors influencing the reversible solid‐state interconversion between the nitro and nitrito structural isomers have also been investigated, providing insight into the dynamics of this process. The cis‐[Ni(dcpe)(NO₂)₂] ( 1 ) and cis‐[Ni(dppe)(NO₂)₂] ( 2 ) complexes show reversible 100 % interconversion between the η¹‐NO₂ nitro isomer and the η¹‐ONO nitrito form when single‐crystals are irradiated with 400 nm light at 100 K. Variable temperature photocrystallographic studies for these complexes established that the metastable nitrito isomer reverted to the ground‐state nitro isomer at temperatures above 180 K. By comparison, the related trans complex [Ni(PCy₃)₂(NO₂)₂] ( 3 ) showed 82 % conversion under the same experimental conditions at 100 K. The level of conversion to the metastable nitrito isomers is further reduced when the nickel centre is replaced by palladium or platinum. Prolonged irradiation of the trans‐[Pd(PCy₃)₂(NO₂)₂] ( 4 ) and trans‐[Pt(PCy₃)₂(NO₂)₂] ( 5 ) with 400 nm light gives reversible conversions of 44 and 27 %, respectively, consistent with the slower kinetics associated with the heavier members of group 10. The mechanism of the interconversion has been investigated by theoretical calculations based on the model complex [Ni(dmpe)Cl(NO₂)].     

Investigation of the rate coefficient for O(3p) + NO2 → O2 + NO

Measurements of the rate coefficient of the reaction (O³P) + NO₂ → O₂ + NO have been made at 296°K and 240°K, using the technique of NO₂* chemiluminescent decay. Values of 9.3 × 10^?12 cm³ molec^?1 sec^?1 at 296°K and 10.5 × 10^?12 cm³ molec^?1 sec^?1 at 240°K were obtained, in excellent agreement with the recent results of Davis, Herron, and Huie [1]. The earlier lower values may have resulted from loss of NO₂ on surfaces.     

Cerium(IV) Nitrate Complexes With Bidentate Phosphine Oxides

The reactions between ceric ammonium nitrate, (NH₄)₂Ce(NO₃)₆, (CAN) and the bidentate phosphine oxides, 4,5-bis(diphenylphosphine oxide)-9,9-dimethylxanthene (L¹), oxydi-2,1-phenylene bis(diphenylphosphine dioxide) (L²), 1,2-bis(diphenylphosphino)ethane dioxide (L³) and 1,4-bis(diphenylphosphino)butane dioxide, L⁴ have been investigated. The crystal structures of the molecular Ce(NO₃)₄L¹ ( 1 ), and ionic [Ce(NO₃)₃L³₂][NO₃]⋅CHCl₃ ( 3 ), [Ce(NO₃)₃L³₂][NO₃] ( 4 ) and the polymeric [Ce(NO₃)₃L⁴_1.5] [NO₃] ( 5 ) and the cerium(III) complex [Ce(NO₃)₂L¹₂][NO₃] ( 2 ) are reported. The thermal stability of the complexes has been examined by thermogravimetry with the gaseous decomposition products analysed by infrared spectroscopy. Evolution of CO₂ is found for both Ce(III) and Ce(IV) complexes with the later also forming NO₂. The formation of the complexes in solution has been studied by ³¹P NMR spectroscopy and further complexes [Ce(NO₃)₃L¹₂]⁺[NO₃]⁻ and [Ce(NO₃)₂L¹₃]²⁺2[NO₃]⁻ identified in CD₃CN solution. The complex ( 1 ) exists as a single molecular species in solution and is stable in dichloromethane whilst ( 3 ) decomposes on standing in both CD₂Cl₂ and CD₃CN to Ce(III) containing species. Complexes of L² have been identified by solution ³¹P NMR spectroscopy and these decompose in solution to give Ce(NO₃)₃L²₂. This study represents the first structural characterisations of Ce(IV) complexes with bidentate phosphine oxides.     

Deactivation of vibrationally excited ozone by O(3P) atoms

Using laser-induced fluorescence of ozone (to measure the rate of disappearance of O₃²) and NO₂ titration (to determine O atom concentrations), we have determined bimolecular rate constants for the deactivation by O(³P atoms) of ozone in excited stretching and bending modes. These experiments do not distinguish between deactivation by (a) the exchange of vibrational and translational energy or (b) the chemical reaction O₃ + O → 2O₂. If the non-reactive pathway (a) is assumed to dominate, then O(³P) is 150 times more effective than O₂ in deactivating O²₃. If chemical reaction (b) is dominant, the bimolecular rate constant for O²₃ + O(³P) is larger by a factor of 150–1500 than that for ground-state ozone.     

Kinetics of the reactions Br + NO2 + M and I + NO2+ M

The reactions Br + NO₂ + M → BrNO₂ + M (1) and I + NO₂ + M → INO₂ + M (2) have been studied at low pressure (0.6-2.2 torr) at room temperature and with helium as the third body by the discharge-flow technique with EPR and mass spectrometric analysis of the species. The following third order rate constants were found k₁₍₀₎ = (3.7 ± 0.7) × 10^?31 and k₂₍₀₎ = (0.95 ± 0.35) × 10^?31 (units are cm⁶ molecule^?2 s^?1). The secondary reactions X + XNO₂ → X₂ + NO₂ (X = Br, I) have been studied by mass spectrometry and their rate constants have been estimated from product analysis and computer modeling.     

Parameter optimization of electrothermal vaporization inductively coupled plasma mass spectrometry for oligoelement determination in standard reference materials

The operational parameters of the graphite furnace for electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS), i.e. the internal carrier gas flow rate, the total carrier gas flow rate, the sample pretreatment temperature and the volatilization temperature, are optimized for oligoelement determinations (⁷⁵As, ⁹Be, ¹¹²Cd, ⁵⁰Cr, ⁶⁵Cu, ¹⁰³Rh, ¹²³Sb). The volatilization temperatures of As and Cr are compared to those obtained by graphite furnace atomic absorption spectrometry (GFAAS). Several modifiers Mg(NO₃)₂, Pd(NO₃)₂, Mg(NO₃)₂/Pd(NO₃)₂, Ni(NO₃)₂, KI, (NH₄)H₂PO₄ have been tested using the concentrations recommended for GFAAS. The concentration of Mg(NO₃)₂ alone and in combination with NaCl has been varied to find the optimal modifier conditions. ETV-ICP-MS signal enhancements by a factor of 10 to 130 respective to those of conventional nebulization have been obtained. The optimized parameters are evaluated by analyzing the water standard reference NIST 1643c and the aqua regia solution of the lake sediment reference material BCR 280.     

Parameter optimization of electrothermal vaporization inductively coupled plasma mass spectrometry for oligoelement determination in standard reference materials

The operational parameters of the graphite furnace for electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS), i.e. the internal carrier gas flow rate, the total carrier gas flow rate, the sample pretreatment temperature and the volatilization temperature, are optimized for oligoelement determinations (⁷⁵As, ⁹Be, ¹¹²Cd, ⁵⁰Cr, ⁶⁵Cu, ¹⁰³Rh, ¹²³Sb). The volatilization temperatures of As and Cr are compared to those obtained by graphite furnace atomic absorption spectrometry (GFAAS). Several modifiers Mg(NO₃)₂, Pd(NO₃)₂, Mg(NO₃)₂/Pd(NO₃)₂, Ni(NO₃)₂, KI, (NH₄)H₂PO₄ have been tested using the concentrations recommended for GFAAS. The concentration of Mg(NO₃)₂ alone and in combination with NaCl has been varied to find the optimal modifier conditions. ETV-ICP-MS signal enhancements by a factor of 10 to 130 respective to those of conventional nebulization have been obtained. The optimized parameters are evaluated by analyzing the water standard reference NIST 1643c and the aqua regia solution of the lake sediment reference material BCR 280.     

Identification of Thermal Decomposition Products and Reactions for Liquid Ammonium Nitrate on the Basis of Ab Initio Calculation

This work analyzed the thermal decomposition of ammonium nitrate (AN) in the liquid phase, using computations based on quantum mechanics to confirm the identity of the products observed in past experimental studies. During these ab initio calculations, the CBS‐QB3//ωB97XD/6–311++G(d,p) method was employed. It was found that one of the most reasonable reaction pathways is HNO₃ + NH₄⁺ → NH₃NO₂⁺ + H₂O followed by NH₃NO₂⁺ + NO₃^– → NH₂NO₂ + HNO₃. In the case in which HNO₃ accumulates in the molten AN, alternate reactions producing NH₂NO₂ are HNO₃ + HNO₃ → N₂O₅ + H₂O and subsequently N₂O₅ + NH₄⁺ → NH₂NO₂ + H₂O. In both scenarios, HNO₃ plays the role of a catalyst and the overall reaction can be written as NH₄⁺ + NO₃^– (AN) → NH₂NO₂ + H₂O. Although the unimolecular decomposition of NH₂NO₂ is thermodynamically unfavorable, water and bases both promote the decomposition of this molecule to N₂O and H₂O. Thus AN thermal decomposition in the liquid phase can be summarized as NH₄⁺ + NO₃^– (AN) → N₂O + 2H₂O.     

Synthesis,Characterization, and Crystal Structures of Cu,Ag, and Pd Dinitramide Salts

The literature known, but not fully characterized, silver dinitramide transfer reagents AgN(NO₂)₂ ( 1 ), [Ag(NCCH₃)][N(NO₂)₂] ( 2 ), and [Ag(py)₂][N(NO₂)₂] ( 3 ) have been investigated by ¹⁰⁹Ag, ¹⁴N NMR and vibrational spectroscopy (IR, Raman). In addition, the poorly understood [Cu(NH₃)₄][N(NO₂)₂)]₂ ( 4 ) and [Pd(NH₃)₄][N(NO₂)₂]₂, ( 5 ) have also been prepared and characterized by ¹⁴N NMR and vibrational spectroscopy (IR, Raman). The structures of 2 — 5 have also been determined by X‐ray diffraction.     

Temperature dependence of the unimolecular decomposition of pernitric acid and its atmospheric implications

The decay of pernitric acid (HO₂NO₂) in the presence of excess nitric oxide has been studied in a 5800-liter, Teflon-lined chamber over the temperature range 254 to 283 K at 1 atm pressure of N₂ by Fourier transform infrared spectroscopy. A heterogeneous reaction of NO₂ and H₂O₂ was used to generate HO₂NO₂ with less than 20% HNO₃ and less than 5% NO₂ present as impurities. The HO₂NO₂ had lifetimes of 5 to 20 h in our chamber, presumably determined by heterogeneous loss to the walls. Two paths have been proposed for the reaction of NO₂ with HO₂:

(1), NO₂ + HO₂ → HONO + O₂ (2). In this study the ratio k₁/k₂ was calculated to be greater than 10³ throughout the temperature range studied. The homogeneous unimolecular decay of the HO₂NO₂, reaction (3), was investigated by adding excess NO in order to remove HO₂ by reaction (4).

(3), HO₂ + NO → NO₂ + OH (4). The rate constant k₃ was determined to be 1.4 × 10¹⁴ exp(?20700 ± 500/RT)s^?1. The thermal decomposition lifetimes of HO₂O₂ at 1 atm total pressure calculated from k₃ are 12 s at 298 K, 5 min at 273 K and 1 month at 220 K. Implications of these results for the role of pernitric acid in the lower and upper atmosphere are discussed.     

Possible production of O2(1Δg) and O2(1Σ+g) in the reaction of NO with O3

High-resolution spectra of the NO₂ continuum emission produced from the reaction NO + O₃ → NO₂ + O₂ have been investigated to detect any possible emission from O₂(¹Δ_g) at 1270 nm or O₂(¹Σ⁺_g) at 762 nm. The photolysis of O₃/O₂ mixtures at 253.7 nm, which produces both states of O₂ with known quantum efficiency, has been used as an internal standard. From the results it is concluded that less than 1/300 and 1/200 of the NO + O₃ reactive collissions result in production of O₂(¹Δ_g) or O₂(¹Σ⁺_g), respectively, at room temperature.     

The n-π transitions of the pyrazine molecule: II. Polarized spectrum in benzene crystal,and anharmonicity in the upper singlet state potential function

The polarized absorption spectra of pyrazine (h₄ and d₄) in single benzene crystals have been measured at high resolution at 2 K. Vibrational assignments in the ¹Ag → ¹B_3u (nπ^*) transition have been confirmed and considerably extended. The quartic potential component of hydrogen bending mode :Oa has been found to originate primarily from vibronic coupling with the nearby ¹B_2u (ππ^*). The coupling between in-plane 6a and out-of-plane 10a modes is described theoretically, and leads to further spectral assignments. Other out-of-plane modes 4 and 5 are identified and shown to have combination defects with 6a. A quartic component found for the out-of-plane ring bending mode 4 could not be explained by vibronic coupling.     

NH(A3Π → X3Σ−) Chemiluminescence from the CH(X2 Π) + NO reaction

NH(A³Π → X³Σ^?) and OH(A²Σ⁺ → X²Π) chemiluminescences from the reaction of CH(X²Π) with NO and O₂, respectively, have been observed at room temperature. From the decay of such emissions we have measured the rate constants for these two reactions: k_NO = (2.5 ± 0.5) × 10^?10 and k_O2 = (8 ± 3) × 10^?11 cm³ molecule ^?1 s^?1, which are in agreement with previously reported rates determined by direct CH(X) detection using, laser-induced fluorescence. This indicates that a four-centered mechanism generating these excited species is operative in both reactions. The CH generation from 266 nm photolysis of CHBr₃ has also been investigated via analysis of CH* emissions.     

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.     

An FTIR spectroscopic study of the reactions Br + CH3CHO → HBr + CH3CO and CH3C(O)OO + NO2 ⇌ CH3C(O)OONO2 (PAN)

Based on an FTIR-product study of the photolysis of mixtures containing Br₂? CH₃CHO and Br₂? CH₃CHO? HCHO in 700 torr of N₂, the rate constant for the reaction Br + CH₃CHO → HBr + CH₃CO was determined to be 3.7 × 10^?12 cm³ molecule^?1 s^?1. In addition, the selective photochemical generation of Br at λ > 400 nm in mixtures containing Br₂? CH₃CHO? ¹⁴NO₂ (or ¹⁵NO₂)? O₂ was shown to serve as a quantitative preparation method for the corresponding nitrogen-isotope labeled CH₃C(O)OONO₂ (PAN). From the dark-decay rates of ¹⁵N-labeled PAN in large excess ¹⁴NO₂, the rate constant for the unimolecular reaction CH₃C(O)OO¹⁵NO₂ → CH₃C(O)OO + ¹⁵NO₂ was measured to be 3.3 (±0.2) × 10^?4 s^?1 at 297 ± 0.5 K.     

Kinetics and mechanism of the reaction of CF3 radicals with NO2

The reaction of CF₃ with NO₂ was studied at 296 ± 2K using two different absolute techniques. Absolute rate constants of (1.6 ± 0.3) × 10⁻¹¹ and (2.1 _−0.3⁺⁰⁷) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ were derived by IR fluorescence and UV absorption spectroscopy, respectively. The reaction proceeds via two reaction channels: CF₃ + NO₂ → CF₂O + FNO, (70 ± 12)% and CF₃ + NO₂ → CF₃O + NO, (30 ± 12)%. An upper limit of 11% for formation of other reaction products was determined. The overall rate constant was within the uncertainty independent of total pressure between 0.4 to 760 torr. © 1996 John Wiley & Sons, Inc.