CN chemiluminescence in N2 + CH4 Flowing afterglow at low temperatures

The spectra of flowing microwave post-discharge excited in N₂ and N₂ + CH₄(N₂ + C₂H₂) gas mixtures have been studied at low temperature (77 K). The molecular spectra of CN emitted by the collision-induced N + C and N + CH chemiluminescent reactions in the low-temperature afterglow system have been thoroughly investigated. The intensity of different CN (B²⁺-X²⁺) vibrational bands is very sensitive to low hydrocarbon concentration in nitrogen used as the working gas. Detection of hydrocarbon species has been demonstrated from concentrations of CH₄ and C₂H₂ in N₂ greater than 10¹⁰ molecules · cm^–3.     

Characterization of the Active Species in the Afterglow of a Nitrogen and Helium Atmospheric-Pressure Plasma

The concentrations of the neutral active species in the afterglow of a nitrogen and helium atmospheric-pressure plasma have been determined by optical emission and absorption spectroscopy and by numerical modeling. For operation with 10 Torr N₂ and 750 Torr He, at 15.5 W/cm³ rf power, 30.4 L/min flow rate, and a neutral temperature of 50°C, the plasma produced 4.8×10¹⁵ cm^–3 of ground state nitrogen atoms, N(⁴S), 2.1×10¹³ cm^–3 of N₂(A³_u), 1.2×10¹² cm^–3 of N₂(B³_g), and 3.2×10⁹ cm^–3 of N₂(C³_u). The concentration of nitrogen atoms and metastable state nitrogen molecules, N₂(A), increased gradually with the rf power and the nitrogen partial pressure. Both the model and experiments indicate that ground-state nitrogen atoms are the dominant active species in the afterglow beyond 2.0 ms.     

Atmospheric chemistry of n‐CH3(CH2)xCN (x = 0–3): Kinetics and mechanisms

Smog chamber/Fourier transform infrared (FTIR) techniques were used to measure the kinetics of the reaction of n‐CH₃(CH₂)_xCN (x = 0–3) with Cl atoms and OH radicals: k(CH₃CN + Cl) = (1.04 ± 0.25) × 10⁻¹⁴, k(CH₃CH₂CN + Cl) = (9.20 ± 3.95) × 10⁻¹³, k(CH₃(CH₂)₂CN + Cl) = (2.03 ± 0.23) × 10⁻¹¹, k(CH₃(CH₂)₃CN + Cl) = (6.70 ± 0.67) × 10⁻¹¹, k(CH₃CN + OH) = (4.07 ± 1.21) × 10⁻¹⁴, k(CH₃CH₂CN + OH) = (1.24 ± 0.27) × 10⁻¹³, k(CH₃(CH₂)₂CN + OH) = (4.63 ± 0.99) × 10⁻¹³, and k(CH₃(CH₂)₃CN + OH) = (1.58 ± 0.38) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ at a total pressure of 700 Torr of air or N₂ diluents at 296 ± 2 K. The atmospheric oxidation of alkyl nitriles proceeds through hydrogen abstraction leading to several carbonyl containing primary oxidation products. HC(O)CN, NCC(O)OONO₂, ClC(O)OONO₂, and HCN were identified as the main oxidation products from CH₃CN, whereas CH₃CH₂CN gives the products HC(O)CN, CH₃C(O)CN, NCC(O)OONO₂, and HCN. The oxidation of n‐CH₃(CH₂)_xCN (x = 2–3) leads to a range of oxygenated primary products. Based on the measured OH radical rate constants, the atmospheric lifetimes of n‐CH₃(CH₂)_xCN (x = 0–3) were estimated to be 284, 93, 25, and 7 days for x = 0,1, 2, and 3, respectively.     

Quenching of the OH and nitrogen molecular emission by methane addition in an Ar capacitively coupled plasma to remove spectral interference in lead determination by atomic fluorescence spectrometry

A new method is proposed to remove the spectral interference on elements in atomic fluorescence spectrometry by quenching of the molecular emission of the OH radical (A²Σ⁺ → X²Π) and N₂ second positive system (C³Π_u → B³Σ_g) in the background spectrum of medium power Ar plasmas. The experiments were carried out in a radiofrequency capacitively coupled plasma (275 W, 27.12 MHz) by CH₄ addition. The quenching is the result of the high affinity of OH radical for a hydrogen atom from the CH₄ molecule and the collisions of the second kind between nitrogen excited molecules and CH₄, respectively. The decrease of the emission of N₂ second positive system in the presence of CH₄ is also the result of the deactivation of the metastable argon atoms that could excite the nitrogen molecules. For flow rates of 0.7 l min^− 1 Ar with addition of 7.5 ml min^− 1 CH₄, the molecular emission of OH and N₂ was completely removed from the plasma jet spectrum at viewing heights above 60 mm. The molecular emission associated to CH and CH₂ species was not observed in the emission spectrum of Ar/CH₄ plasma in the ultraviolet range. The method was experimented for the determination of Pb at 283.31 nm by atomic fluorescence spectrometry with electrodeless discharge lamp and a multichannel microspectrometer. The detection limit was 35 ng ml^− 1, 2–3 times better than in atomic emission spectrometry using the same plasma source, and similar to that in hollow cathode lamp microwave plasma torch atomic fluorescence spectrometry.     

Energy disposal in the photodissociation HCN(Ã1A″) → H + CN(X 2Σ) at 193 nm

Rotational energy disposal has been measured in CN(X ²Σ, υ″ = 0, 1, 2) following 193 nm dissociation of HCN vapor at 295 K. The fractional populations for the three vibrational states are 0.56 ± 0.08, 0.33 ± 0.13, and 0.11 ± 0.03 for υ″ = 0, 1 and 2 respectively. This distribution is fit well by a Poisson distribution with an average vibrational quantum number of 0.55 corresponding to the average vibrational energy of 1128 ± 294 cm⁻¹. This energy represents (10 ± 3)% of the available energy. The rotational distributions in all three vibrational states can be represented by a single surprisal which depends linearly on N″/N″_max where N″_max is the maximum value of the rotational quantum number permitted by energy conservation and the prior distribution is similarly constrained. The average energy in rotation is 1055 ± 373 cm⁻¹ which represents (9 ± 3)% of that available for disposal. Time-dependence measurements indicate that product CN(X ²Σ, υ = 0) is formed in both a fast (τ < 80 ns) and a slow process. No evidence is found for the production of CN(A ²Π, υ ≈ 0).     

Etude par diffraction X et par spectrometrie de vibration de composes de coordination des halogenures d'aluminium avec l,acetonitrile: analyse vibrationnelle des cations AlCl(CH3CN)2+5 et AlBr(CH3CN)52+

The compounds AlX₃-2CH₃CN and AlX₃-1.66CH₃CN (X = Cl, Br) are prepared in order to study the vibrational properties of AlX(CH₃CN)²⁺₅. The different chemical phases obtained are characterised by X-ray diffraction. It is shown that AlCl₃-2CH₃CN and AlBr₃-2CH₃CN are isomorphic and unit cell parameters are determined. The spectra of the cations AlX(CH₃CN)²⁺₅ in the 600-50cm^?1 range are interpreted by comparison with those of Al(CH₃CN)³⁺₆ and from the data obtained from H-D substitution. Analysis of the spectra of the complexes AlX₃-1,66CH₃CN enables the formula [2AlX^?₄: AlX(CH₃CN)|²⁺₅] to be postulated.     

Bond length of perchlorate at different temperatures: X‐ray and neutron comparison

The averages (average deviations from the mean are given in square brackets) of uncorrected Cl—O bond distances in a perchlorate anion from an X‐ray diffraction analysis of (N‐{2‐[bis(pyridin‐2‐ylmethyl)amino]ethyl}pyridine‐2‐carboxamidato)(nitric oxide)manganese perchlorate acetonitrile disolvate, [Mn(C₂₀H₂₀N₅O)(NO)]ClO₄·2CH₃CN or [Mn(PaPy₃)(NO)]ClO₄·2CH₃CN, decrease from 1.447 [4] Å at 10 K to 1.428 [4] Å at 170 K. The 10 K value is close to the neutron value (1.441 [1] Å) at 18 K. Comparisons are made with a second X‐ray study at 30 K [1.444 (8) Å] and to libration‐corrected, density functional theory (DFT), and Cambridge Structural Database (CSD) values.     

In situ FTIR diagnostics of the radio-frequency plasma decomposition of N2O

The decomposition of N₂O in a 13.56-MHz parallel-plate system was studied usingin situ Fourier transform infrared (FTIR) spectroscopy. Areas of two infrared absorption bands of N₂O recorded at 8 cm^–1 resolution were used to estimate relative gas-phase dissociation as a function of rf power and flow rate at 500 mT. Flow rate was found to strongly affect band areas over the range of powers investigated (10–90 W). The effect of rf power on band areas diminished above 40 W, probably due to poor plasma confinement. Distortion of the band shapes by the plasma permitted rotational temperatures to be estimated. Rotational temperature increased essentially linearly with power at constant flow rate, reaching 450 K at 80 W, but was independent of flow rate at constant power. Rotational temperatures were also found to depend on the temperature of the electrodes, which were heated by plasma exposure. No infrared-active product species were observed even under batch conditions where all N₂O was irreversibly dissociated. This lack of detectable products and a 50% pressure rise observed in a batch study suggest that N₂ and O₂ are the primary stable discharge products.     

Kinetic study of the reaction of CH3O with Br and Br2

The title reactions have been studied at room temperature by applying the discharge flow method coupled with laser induced fluorescence detection of methoxy radicals and resonance fluorescence detection of bromine atoms. The following rate constants were determined: CH₃O + Br Õ products (1) k ₁ (298 K) = (3.4 ± 0.4 (1)) × 10¹³ cm³ mol^-1 s^-1, CH₃O + Br₂ Õ products (2) k ₂ (298 K) £ 5 × 10⁸ cm³ mol^-1 s^-1.     

Rate Constant for the Reaction of the OH-Radical with CH2F2

The rate constant value of k ₁ = (6.05 ± 0.20)×10⁹ cm³ mol^–1 s^–1 (with ± 1 error) has been determined for the reaction OH + CH₂F₂ (1) by applying the discharge-flow/resonance-fluorescence method at 298 K.     

Kinetics of CN radical reactions with formaldehyde and 1,3,5-trioxane

Absolute rate constants were measured for the reaction CN + CH₂O over the temperature range 297–673 K and CN + 1,3,5-trioxane over the range of 297–600 K by the laser photolysis/laser induced fluorescence technique. The rate constants for these reactions can be effectively represented, in units of cm³/s, by: k(CH₂O) = 2.82 × 10^?19 T^2.72 exp(718/T), and k(1,3,5-trioxane) = 1.39 × 10^?23 T^4.26 exp(1333/T), respectively. Transition state theory calculations were able to fit the temperature dependence of the CN + CH₂O rates relatively well. We attempted to correlate the CN reaction rate with CH₂O and other molecules which occur through simple abstraction with the corresponding OH reaction rates, yielding only a qualitative linear correlation for a majority of the processes. The reactions which deviated significantly from linearity include those which contain strong dipoles, highlighting the significant role long-range attractive forces play in CN and OH reactions. Using a simple electrostatic potential, cross-sections were determined for reactions with CN. No linear correlation was found between the calculated and experimental cross sections for the majority of the reactions studied. © 1993 John Wiley & Sons, Inc.     

Synthese und Eigenschaften von (Acido)(nitrosyl)phthalocyaninato(2–)ruthenium

Synthesis and Properties of (Acido)(nitrosyl)phthalocyaninato(2–)ruthenium (Acido)(nitrosyl)phthalocyaninato(2–)ruthenium, [Ru(X)(NO)pc^2–] (X = F, Cl, Br, I, CN, NCO, NCS, NCSe, N₃, NO₂) is obtained by acidification of a solution of bis(tetra(n-butyl)ammonium) bis(nitro)phthalocyaninato(2–)ruthenate(II) in tetrahydrofurane with the corresponding conc. mineral acid or aqueous ammonium salt solution. The nitrite-nitrosyl conversion is reversal in basic media. The cyclic and differential pulse voltammograms show mainly three quasi-reversible one-electron processes at 1.05, –0.65 and –1.25 V, ascribed to the first ring oxidation and the stepwise reduction to the complexes of type {RuNO}⁷ and {RuNO}⁸, respectively. The B < Q < N regions in the electronic absorption spectra are still typical for the pc^2– ligand, but are each split into two strong absorptions (14500/16500(B); 28000/30500(Q); 34500/37000 cm^–1(N)), whose relative intensities strongly depend on the nature of the axial ligand X. In the IR spectra is active the N–O stretching vibration between 1827 (X = I) and 1856 cm^–1 (F), the C–N stretching vibration at 2178 (X = NCO), 2072 (NCS), 2066 (NCSe), 2093 cm^–1 (CN), the N–N stretching vibration of the azide ligand at 2045 cm^–1, the fundamentals of the nitrito(O) ligand at 1501, 932, and 804 cm^–1, and the Ru–X stretching vibration at 483 (F), 332 (Cl), 225 (Br), 183 (I), 395 (N₃), 364 (ONO), 403 (CN), 263 (NCS), and 231 cm^–1 (NCSe). In the resonance Raman spectra, excited in coincidence with the B region, the Ru–NO stretching vibration and the very intense Ru–N–O deformation vibration are selectively enhanced between 580 and 618 cm^–1, and between 556 and 585 cm^–1, respectively.     

Raman and Infrared Spectra, Ab Initio Calculations, Normal Coordinate Analysis, and Conformational Stability of 2-Methoxypropene

The Raman (3500–40 cm^–1) and infrared (3500–70 cm^–1) spectra of gaseous and solid 2-methoxypropene, CH₃O(CH₃)C=CH₂, and the isotopomers, CD₃O(CH₃)C=CH₂ and CH₃O(CD₃)C=CD₂ have been recorded. In addition, the Raman spectra of the liquids have been recorded with qualitative depolarization measurements. All of these data indicate that only one conformer is present in the fluid phases at ambient temperature and this form is the cis conformer, which remains in the solid. Assignments are provided for the fundamentals of all three isotopomers for the cis conformer with C_s symmetry. The far-infrared spectra of all three isotopic species have been recorded at a resolution of 0.1 cm^–1 in the gas and 1.0 cm^–1 in the solid. The parameters of the potential function governing the asymmetric torsion are determined to be V₃ = 1485 ± 9 cm^–1 and V₆ = –55 ± 4 cm^–1 for the d₀ compound, where only two terms were determined, since a second conformer was not evident. The barrier to internal rotation for the methyl group attached to the oxygen atom is 1370 ± 8 cm^–1 and the C—CH₃ barrier is 772 ± 5 cm^–1. Ab initio calculations with full electron correlation have been carried out by the perturbation method to second order to obtain the equilibrium structural parameters, harmonic force constants, fundamental frequencies, infrared intensities, Raman activities, depolarization values, and conformational stability. The predicted values have been compared to the experimental values where appropriate.     

Computational Studies of Coinage Metal Anion M− + CH3X (X = F,Cl, Br,I) Reactions in Gas Phase

We characterized the stationary points along the nucleophilic substitution (S_N2), oxidative insertion (OI), halogen abstraction (XA), and proton transfer (PT) product channels of M⁻ + CH₃X (M = Cu, Ag, Au; X = F, Cl, Br, I) reactions using the CCSD(T)/aug-cc-pVTZ level of theory. In general, the reaction energies follow the order of PT > XA > S_N2 > OI. The OI channel that results in oxidative insertion complex [CH₃–M–X]⁻ is most exothermic, and can be formed through a front-side attack of M on the C-X bond via a high transition state OxTS or through a S_N2-mediated halogen rearrangement path via a much lower transition state invTS. The order of OxTS > invTS is inverted when changing M⁻ to Pd, a d¹⁰ metal, because the symmetry of their HOMO orbital is different. The back-side attack S_N2 pathway proceeds via typical Walden-inversion transition state that connects to pre- and post-reaction complexes. For X = Cl/Br/I, the invS_N2-TS’s are, in general, submerged. The shape of this M⁻ + CH₃X S_N2 PES is flatter as compared to that of a main-group base like F⁻ + CH₃X, whose PES has a double-well shape. When X = Br/I, a linear halogen-bonded complex [CH₃−X∙··M]⁻ can be formed as an intermediate upon the front-side attachment of M on the halogen atom X, and it either dissociates to CH₃ + MX⁻ through halogen abstraction or bends the C-X-M angle to continue the back-side S_N2 path. Natural bond orbital analysis shows a polar covalent M−X bond is formed within oxidative insertion complex [CH₃–M–X]⁻, whereas a noncovalent M–X halogen-bond interaction exists for the [CH₃–X∙··M]⁻ complex. This work explores competing channels of the M⁻ + CH₃X reaction in the gas phase and the potential energy surface is useful in understanding the dynamic behavior of the title and analogous reactions.     

An ab initio calculation of 14n quadrupole coupling constants

Ab initio SCF-MO calculations of ¹⁴N quadrupole coupling constants are reported for HCN, HNC, CH₃CN, CH₃NC, NH₃, NH₂NH₂, FCN, N₂O, (CN)₂, BrCN, pyridine and pyrazine. There is excellent correlation between calculation and experiment yielding Q = 1.503 ± 0.159 × 10^?26 cm² for the ¹⁴N nuclear quadrupole moment. Dunning sp basis sets are more than adequate for such calculations, STO/4G basis sets yielding almost identical results for pyridine and pyrazine. Unsuccessful attempts were made to correlate coupling constants with electronic population analysis indices.     

An ab initio molecular orbital study of the deprotonation of amines

The geometries of the amines NH₂X and amido anions NHX^?, where X = H, CH₃, NH₂, OH, F, C₂H, CHO, and CN have been optimized using ab initio molecular orbital calculations with a 4-31G basis set. The profiles to rotation about the N? X bonds in CH₃NH^?, NH₂NH^?, and HONH^? are very similar to those for the isoprotic and isoelectronic neutral compounds CH₃OH, NH₂OH, and HOOH. The amines with unsaturated bonds adjacent to the nitrogen atoms undergo considerable skeletal rearrangement on deprotonation such that most of the negative charge of the anion is on the substituent. The computed order of acidity for the amines NH₂X is X = CN > HCO > F ≈ C₂H > OH > NH₂ > CH₃ > H and for the reaction NHX^? + H⁺ → NH₂X the computed energies vary over the range 373–438 kcal/mol.     

Regioselective Sequential Additions of Nucleophiles and Electrophiles to Perfluoroalkylfullerenes: Which Cage C Atoms Are the Most Reactive and Why?

The sequential addition of CN^? or CH₃^? and electrophiles to three perfluoroalkylfullerenes (PFAFs), C_s‐C₇₀(CF₃)₈, C₁‐C₇₀(CF₃)₁₀, and C_s‐p‐C₆₀(CF₃)₂, was carried out to determine the most reactive individual fullerene C atoms (as opposed to the most reactive C?C bonds, which has previously been studied). Each PFAF reacted with CH₃^? or CN^? to generate metastable PFAF(CN)^? or PFAF(CH₃)₂^2? species with high regioselectivity (i.e., one or two predominant isomers). They were treated with electrophiles E⁺ to generate PFAF(CN)(E) or PFAF(CH₃)₂(E)₂ derivatives, also with high regioselectivity (E⁺=CN⁺, CH₃⁺, or H⁺). All of the predominant products, characterized by mass spectrometry and ¹⁹F NMR spectroscopy, are new compounds. Some could be purified by HPLC to give single isomers. Two of them, C₇₀(CF₃)₈(CN)₂ and C₇₀(CF₃)₁₀(CH₃)₂(CN)₂, were characterized by single‐crystal X‐ray diffraction. DFT calculations were used to propose whether a particular reaction is under kinetic or thermodynamic control.     

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.     

Kinetic study of the oxidation reaction of 4-methylphenyl radical

A kinetic study of the reaction of the 4-methylphenyl radical (4-C₆H₄CH₃) with the oxygen molecule was conducted using experimental and theoretical approaches. The absorption spectrum for the λ = 266 nm photolysis of the 4-C₆H₄CH₃X (X = Cl, Br)/N₂/O₂ mixture was measured in the wavelength range of λ = 503-512 nm using N₂ as the buffer gas at a total pressure of 40 Torr using a cavity ring-down spectroscopy apparatus coupled with a pulsed laser photolysis system. Based on the absorbance of the product of the 4-C₆H₄CH₃ + O₂ reaction at λ = 504 nm, the reaction rate coefficient for the 4-C₆H₄CH₃ + O₂ reaction was determined to be k = (1.21 ± 0.10) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and k = (1.18 ± 0.21) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ using 4-C₆H₄CH₃Cl and 4-C₆H₄CH₃Br, respectively, as the radical precursor. And there was no pressure dependence in the total pressure range of 10-90 Torr varying partial pressure of N₂ buffer gas at T = 296 ± 5 K. The geometries, vibration frequencies, and potential energy surfaces of the reactants, major products, and transition states in the 4-C₆H₄CH₃ + O₂ reaction were determined using the CBS-QB3 method. The k value at the high-pressure limit was calculated to be 1.26 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ using the variational transition-state theory. The calculated value of k was consistent with the experimental value, which indicated that the 4-C₆H₄CH₃ + O₂ reaction reaches the high-pressure limit at 10 Torr. Therefore, the oxidation of the 4-C₆H₄CH₃ radical is almost 10 times faster than that of the benzyl radical, which has the same chemical formula, at the high-pressure limit.     

Thermal ignition of acetonitrile. Experimental results and kinetic modeling

Ignition delay times of acetonitrile (CH₃CN) in mixtures containing acetonitrile and oxygen diluted in argon were studied behind reflected shock waves. The temperature range covered was 1420–1750 K at overall concentrations behind the reflected shock wave ranging from 2 to 4×10⁻⁵ mol/cm³. Over this temperature and concentration range the ignition delay times varied by approximately one order of magnitude, ranging from ca. 100 μs to slightly above 1 ms. From a total of some 70 tests the following correlation for the ignition delay times was derived: t_ign=9.77×10⁻¹² exp(41.7×10³/RT)×{[CH₃CN]^0.12[O₂]^−0.76[Ar]^0.34} s, where concentrations are expressed in units of mol/cm³ and R is expressed in units of cal/(K mol). The ignition delay times were modeled by a reaction scheme containing 36 species and 111 elementary reactions. Good agreement between measured and calculated ignition delay times was obtained. A least-squares analysis of 60 computed ignition delay times from six different groups of initial conditions gave the following temperature and concentration dependence: E=46.2×10³ cal/mol, β=0.43, β=−1.18, and β_Ar=0.18. The ignition process is initiated by H-atom ejection from acetonitrile. The addition of oxygen atoms to the system from the dissociation of molecular oxygen and from the reaction CH₃CN+O₂ → HO₂·+CH₂CN·is negligible. In view of the relatively high concentration of methyl radicals obtained in the reaction CH₃CN+H → CH₃+HCN, the branching step CH₃+O₂ → CH₃O+O plays a more important role than the parallel step H+O₂→ OH+O. A discussion of the mechanism in view of the sensitivity analysis is presented. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 839–849, 1997