Kinetics of the reaction of NH2 with NO2

The absolute rate constant of the reaction of NH₂ with NO₂ has been measured using a flash-photolysis laser resonance-fluorescence technique. The value obtained at room temperature is k₁ = 2.3 (± 0.2) × 10^?11 cm³ molecule ^?1 s^?1. A negative temperature coefficient has been found between 298 and 505 K for this reaction, k₁ = 3.8 × 10^?8 × T^?1.30 cm³ molecule^?1 s^?1. It is thought that this is the major reaction of NH₂ in the troposphere.     

The multichannel reaction NH2 + NH2 at ambient temperature and low pressures

NH₂ profiles were measured in a discharge flow reactor at ambient temperature by monitoring reactants and products with an electron impact mass spectrometer. At the low pressures used (0.7 and 1.0 mbar) the gas-phase self-reaction is dominated by a ‘bimolecular’ H₂-eliminating exit channel with a rate coefficient of k_3b(300 K) = (1.3 ± 0.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and leading to N₂H₂ + H₂ or NNH₂ + H₂. Although the wall loss for NH₂ radicals is relatively small (k_w ≈ 6–14 s⁻¹), the contribution to the overall NH₂ decay is important due to the relatively slow gas-phase reaction. The heterogeneous reaction yields N₂H₄ molecules.     

Rates of reaction of NH2 with N,NO AND NO2

The decay of NH₂ radicals, from 193 nm photolysis of NH₃, was monitored by 597.7 nm laser-induced fluorescence. Room-temperature rate constants of (1.21 ± 0.14) × 10^?10, (1.81 ± 0.12) × 10^?11, and (2.11 ± 0.18) × 10^?11 cm³ molecule^?1 s^?1 were obtained for the reactions of NH₂ with N, NO and NO₂, respectively. The production of NH in the reaction of NH₂ with N was observed by laser-induced fluorescence at 336.1 nm.     

Determination of the rate constant for the reaction NH3 + OH → NH2 + H2O

The rate constant for the reaction NH₃ + OH → NH₂ + H₂O was determined by the comparison of the calculated induction period data with experiments by the shock tube technique in the range 1360–1840 K, for NH₃-H₂-O₂-Ar mixtures. The rate constants can be represented by the expression k = 10^12.49±0.04exp[(?1.95±0.15) kcal/,RT] cm³ mol^?1 s^?1.     

Flash photolysis studies of the reaction of NH2 radicals with NO

The kinetics of the reaction NH₂ + NO → N₂ + H₂O were studied, using a conventional flash photolysis system. A value of k₁ = (1.1 ± 0.2) × 10¹⁰ & mole^?1 s^?1 was obtained at room temperature and in the pressure range 2–700 torr in the presence of nitrogen. A slight negative temperature coefficient was observed between 300 and 500 K, equivalent to a negative activation energy of 1.05 ± 0.2 kcal mole^?1.     

Internal-energy-selected measurements on the relative cross section of the ion-molecule reaction NH3+(NH3, NH2)NH4+

A photoelectron-photoion coincidence technique is used to measure the internal-energy dependence of the ion-molecule reaction NH₃⁺(E_int+NH₃ → NH₄⁺ + NH₂ at thermal collision energy. The range in which the internal energy is varied, is enlarged by including in the experiment the electronically excited state of the NH₃⁺ ion. Special attention is paid to the possible influence of the product's kinetic energy on the measurements. The experimental results are analysed using a modified statistical model and compared with previous data.     

Rate constant for the reaction NH3 + OH → NH2 + H2O over a wide temperature range

The rate constant for the reaction or NH₃ + OH → NH₂ + H₂O has been measured in a high temperature fast flow reactor over the range 294–1075 K k = (5.41 ± 0.86) × 10^-12 exp[?(2120 ± 143) cal mole^?1/RT cm³ molecule^?1 s^?1. This result is compared with literature values and discussed.     

Kinetic mass spectrometric determination of the absolute rate coefficient for the reaction NH3 (ν = 0) + NH3 → NH4 + NH2 at thermal kinetic energies

The absolute thermal rate coefficient for the reaction NH₃⁺ + NH₃ → NH₄⁺ + NH₂ has been determined experimentally for the first time for NH₃⁺ (ν = 0) reactant ions. An increase in E_vib results in a decrease in the rate coefficient for proton transfer.     

DSC investigation of the thermal behaviour of (NH4)2SO4, NH4HSO4 and NH4NH2SO3

Gaseous products evolved from (NH₄)₂SO₄, NH₄HSO₄ and NH₄NH₂SO₃ during successive heating and cooling cycles were flushed with inert gas into analyzer Dräger tubes hooked tightly to the terminal port of the DSC cell base. This simple procedure allowed the starting temperature of the decomposition to be determined and the amount of the individual gases in the mixture to be identified and even estimated. NH₄NH₂SO₃ at 523 K in humid air produced HNH₂SO₃ initially and, on further cycling, (NH₄)₂SO₄ and NH₄HSO₄ also appeared. The ΔH_f values for NH₄HSO₄ were (kJ mole^?1): in an airtight sample holder 12.67, in a dry argon atmosphere 11.93, and in a static air atmosphere 10.92. Endothermic peaks for (NH₄)₂SO₄ and 498 and 411 K represented the incongruent melting point and the polymorphic transition of (NH₄)₂SO₄·NH₄HSO₄. After the first heating in air to 530 K, (NH₄)₂SO₄ and NH₄HSO₄ exhibited closely similar cyclic DSC curves. The endothermic peaks at about 393–420 K may be assigned to different combinations of (NH₄)₂SO₄ and NH₄HSO₄.     

Laser fluorescence of NH2 and rate constant measurement of NH2 + NO

Laser induced fluorescence from the òA₁ state of the NH₂ radical, obtained by different methods, has been observed with a tunable cw dye laser as excitation source. Using pulsed photolysis of NH₃ to produce NH₂, the fluorescence technique has been employed in a first gas kinetic application to measure the rate constant of the aeronomically interesting NH₂ + NO reaction at 298 K. A value of (2.1 ± 0.2) × 10^-11 cm³ molecule^-1 s^-1 has been obtained.     

A re-interpretation of the crystal structure of ‘(NH4)2(NH3)[Ni(NH3)2Cl4]’ in terms of (NH4)2−2z[Ni(NH3)2]z[Ni(NH3)2Cl4]

A re-interpretation and re-evaluation of single-crystal X-ray diffraction data of a previously reported ‘(NH₄)₂(NH₃)[Ni(NH₃)₂Cl₄]’ (J. Solid State Chem. 162 (2001) 254) give a new formula (NH₄)_2−2z[Ni(NH₃)₂]_z[Ni(NH₃)₂Cl₄] with z=0.152. This new formula results from defects in an idealized ‘(NH₄)₂[Ni(NH₃)₂Cl₄]’ basic structure, where two adjacent NH₄⁺ cations are replaced by one Ni(NH₃)₂²⁺ unit. Cl⁻ anions from the basic structure complete the coordination sphere of the new Ni²⁺ to [Ni(NH₃)₂Cl₄]²⁻.     

The role of NH3 atmosphere in preparing nitrogen-doped TiO2 by mechanochemical reaction

NH₃ atmosphere in ball milling plays an important role in preparing TiO_2−XN_X by a simple mechanochemical reaction. The results show that the structure transformation of titania milled in NH₃ is greatly delayed compared with that in air. The specific surface area of titania milled in NH₃ for 2 h is two times larger than that in air. It was also found that titania prepared in NH₃ has obvious absorbance for visible light. Mechanochemical milling in NH₃ atmosphere offers a new route to prepare TiO_2−XN_X with high surface area.     

Ab initio CI study of the reaction between NH2 and NO

Using ab initio CI calculations we have evaluated the structural, energetic and kinetic parameters of the reaction between NH₂ and NO. In light of the results obtained, it appears that while the formation of molecular nitrogen is highly probable, the reaction pathway leading to N₂H+OH cannot be thermodynamically excluded. The kinetic model based on the RRKM and TST methods leads to a calculated rate constant at 298 K (k = 1.64×10⁻¹¹ cm³ molecule⁻¹ s⁻¹) which is comparable to that determined experimentally and which decreases with temperature in the range 200–700 K.     

Ab initio study on the mechanism of reaction HNCO+NH2

Ab initio UMP2 and UQCISD(T) calculations, with 6-311G** basis sets, were performed for the titled reactions. The results show that the reactions have two product channels: NH₂+ HNCO?NH₃+NCO (1) and NH₂+HNCO?N₂H₃+CO (2), where reaction (1) is a hydrogen abstraction reaction via an H-bonded complex (HBC), lowering the energy by 32.48 kJ/mol relative to reactants. The calculated QCISD(T)//MP2(full) energy barrier is 29.04 kJ/mol, which is in excellent accordance with the experimental value of 29.09 kJ/mol. In the range of reaction temperature 2300–2700 K, transition theory rate constant for reaction (1) is 1.68×10¹¹–3.29×10¹¹ mL·mol^-1·s^-1, which is close to the experimental one of 5.0×10¹¹mL·mol^-1·s^-1or less. However, reaction (2) is a stepwise reaction proceeding via two orientation modes,cis andtrans, and the energy barriers for the rate-control step at our best calculations are 92.79 kJ/mol (forcis-mode) and 147.43 kJ/mol (fortrans-mode), respectively, which is much higher than reaction (1). So reaction (1) is the main channel for the titled reaction.     

Theoretical investigations on the SO2 + HO2 reaction and the SO2–HO2 radical complex

The mechanism of the SO₂ + HO₂ reaction was studied theoretically for the first time. Three product channels were revealed, namely, O₂ + HOSO, O₂ + HSO₂, and OH + SO₃. The O₂ + HOSO channel dominates the reaction under combustion conditions. A five-member-ring complex [SO₂–HO₂] exists at the entrance of the reaction. The structure and binding energy (D_e and D₀) of the SO₂–HO₂ complex have been calculated. In view of D₀ = 21.2 ± 2.0 kJ mol⁻¹, the SO₂–HO₂ complex should be stable at low temperature. The infrared spectra and frequency shifts were calculated for both SO₂–HO₂ and SO₂–DO₂, and compared with the available experimental data.     

Hindered rotation of the ammonium ion in (NH4)2SiF6 and (NH4)2SnCl6

The heat capacity due to the hindered rotation of the ammonium ion has been computed for (NH₄)₂SiF₆ and (NH₄)₂SnCl₆ and compared to that derived from the observed heat capacity. The torsional frequencies for (NH₄)₂SiF₆ and (NH₄)₂SnCl₆ are 226 cm^?1 and 190 cm^?1 respectively, and the barriers to rotation are 3210 calories/mole and 1470 calories/mole, respectively.     

Thermal behaviour of (NH4)3VO2F4 and Na(NH4)2VO2F4

The thermal behaviour of (NH₄)₃VO₂F₄ and Na(NH₄)₂VO₂F₄ was investigated using TG, DTA and DSC techniques. The occurrence of a first order phase transition with the onset of decomposition in both the compounds is confirmed. The temperature, energetics and hysteresis of the transition are obtained. A possible path for the thermal degradation is given for both the compounds, and the residues are identified.     

Zur colorimetrischen Bestimmung von HNO2, H2N2O2, NH2OH und NH4OH nebeneinander

Ohne Zusammenfassung     

Spectroscopic properties of guanidinium zinc sulphate [C(NH2)3]2Zn(SO4)2 and ab initio calculations of [C(NH2)3]2 and HC(NH2)3

Raman and FTIR spectra of guanidinium zinc sulphate [C(NH₂)₃]₂Zn(SO₄)₂ are recorded and the spectral bands assignment is carried out in terms of the fundamental modes of vibration of the guanidinium cations and sulphate anions. The analysis of the spectrum reveals distorted SO₄²⁻ tetrahedra with distinct S–O bonds. The distortion of the sulphate tetrahedra is attributed to Zn–O–S–O–Zn bridging in the structure as well as hydrogen bonding. The CN₃ group is planar which is expressed in the twofold symmetry along the C–N (1) vector. Spectral studies also reveal the presence of hydrogen bonds in the sample. The vibrational frequencies of [C(NH₂)₃]₂ and HC(NH₂)₃ are computed using Gaussian 03 with HF/6-31G* as basis set.     

NH2 radicals trapped in NH3 single crystals and various polycrystalline ammonia matrices

?H₂ radical trapped in various ammonia matrices has been investigated by ESR spectroscopy. From the study of the coupling tensors of the ?H₂ radical in a single crystal of NH₃, and taking into account the motions of this radical, it is shown that for all these matrices the spectra can be interpreted on the basis of coupling tensors which give for all cases the same isotropic coupling constants: a_N = 11.3 G, a_H = 24.6 G. Nitrogen and hydrogen coupling tensors for the motionless ?H₂ radical are also discussed