Vibrational spectra,force fields and NMR-data for triorganyl-tetrelomethanes CH4−n(TtR3)n (Tt = Sn and Pb)

Based on vibrational spectra normal coordinate calculations have been carried out for trimethyltetrelomethanes CH_4−n(TtMe₃)_n (Tt = Sn and Pb, n = 2 and 4). The resulting comparable force constants of the two distinguishable types of carbon-metal bonds for Tt = Sn (range K(C-Sn) 220 - 180 Nm⁻¹) are 10 – 15% higher than for Tt = Pb (K(C-Pb) 190 - 170 Nm⁻¹). These force constants K(C-Tt) are similar to the K(C-Hg) values of corresponding methylmercuriomethanes CH_4−n(HgMe)_n. The force constants K (C-Tt), and also the coupling constants ¹J(Tt,C) from NMR spectra, indicate weakening of the carbon-metal bonds in the central CTt_n groups with growing n, whereas the peripheral TtMe bonds are almost unaffected by variations of n.     

Force constants,coriolis coupling constants and mean amplitudes of vibration of GaF63− and FeF63−

The force constants, Coriolis coupling constants and mean amplitudes of vibration at 0, 298.16 and 500 K for GaF₆^3?FeF₆^3? have been reported for the first time employing recent vibrational data. The results are discussed in the light of available information.     

Rate constants and Arrhenius parameters for the reactions of Cl atoms with the halogenated ethers: CF3CH2OCHF2, CF3CHClOCHF2, and CF3CH2OCClF2

Rate constants have been determined for the reactions of Cl atoms with the halogenated ethers CF₃CH₂OCHF₂, CF₃CHClOCHF₂, and CF₃CH₂OCClF₂ using a relative‐rate technique. Chlorine atoms were generated by continuous photolysis of Cl₂ in a mixture containing the ether and CD₄. Changes in the concentrations of these two species were measured via changes in their infrared absorption spectra observed with a Fourier transform infrared (FTIR) spectrometer. Relative‐rate constants were converted to absolute values using the previously measured rate constants for the reaction, Cl + CD₄ → DCl + CD₃. Experiments were carried out at 295, 323, and 363 K, yielding the following Arrhenius expressions for the rate constants within this range of temperature:Cl + CF₃CH₂OCHF₂: k = (5.1₅ ± 0.7) × 10⁻¹² exp(−1830 ± 410 K/T) cm³ molecule⁻¹ s⁻¹ Cl + CF₃CHClOCHF₂: k = (1.6 ± 0.2) × 10⁻¹¹ exp(−2450 ± 250 K/T) cm³ molecule⁻¹ s⁻¹ Cl + CF₃CH₂OCClF₂: k = (9.6 ± 0.4) × 10⁻¹² exp(−2390 ± 190 K/T) cm³ molecule⁻¹ s⁻¹ The results are compared with those obtained previously for the reactions of Cl atoms with other halogenated methyl ethyl ethers. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 165–172, 2001     

Kinetics of Gold Dissolution in Thiosemicarbazide Solutions

The kinetics of gold dissolution in thiosemicarbazide solutions was studied relative to the ratio of ferric ion and thiosemicarbazide concentrations as well as pH. The composition of the complex formed was found to be [Au(NH₂)₂NHC=S₃]⁺. The rate constants for gold dissolution were determined at 278-298 K along with the stability, dissociation, and equilibrium constants at 288 K. The activation energy at 288 K was also found.     

Thermal decomposition of CH3I using I-atom absorption

The recently developed I-atom atomic resonance absorption spectrometric (ARAS) technique has been used to study the thermal decomposition kinetics of CH₃I over the temperature range, 1052–1820 K. Measured rate constants for CH₃I(+Kr)→CH₃+I(+Kr) between 1052 and 1616 K are best expressed by k(±36%)=4.36×10⁻⁹ exp(−19858 K/T) cm³ molecule⁻¹ s⁻¹. Two unimolecular theoretical approaches were used to rationalize the data. The more extensive method, RRKM analysis, indicates that the dissociation rates are effectively second-order, i.e., the magnitude is 61–82% of the low-pressure-limit rate constants over 1052–1616 K and 102–828 torr. With the known E₀=ΔH₀⁰=55.5 kcal mole ⁻¹, the optimized RRKM fit to the ARAS data requires (ΔE)_down=590 cm⁻¹. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 535–543, 1997.     

Temperature dependence of the relaxation rate constants of the a 1Δg and b 1Σ +g states of oxygen isotopes

The relaxation rate constants of the low-lying electronic singlet states, a ¹Δ_g and b ¹Σ⁺_g , of gaseous natural O₂ and of the isotope ¹⁸O₂ were investigated as a function of temperature from 100 to 295 K. The measured increase of the rate constants with temperature is in good agreement with a theory of electronic-to-vibrational-translational energy transfer. The significant effects of the different electronic states and of the isotope masses on the absolute values of the relaxation rate constants, which range from 1.0× 10⁻²⁰ to 3.9× 10⁻¹⁷ s⁻¹ molecule⁻¹ cm³ at 295 K, are discussed.     

Rate constants for the gas-phase reactions of Cl atoms with a series of hydrofluorocarbons and hydrochlorofluorocarbons at 298 ± 2 K

A relative rate method has been used to determine rate constants for the gas-phase reactions of a series of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) at 298 ± 2 K and atmospheric pressure of air. Based on a rate constant for the reaction of the Cl atom with CH₄ of (1.0 ± 0.2) ? 10^?13 cm³ molecule^?1 s^?1 at 298 K, the following Cl atom reaction rate constants (in units of 10^?15 cm³ molecule^?1 s^?1) were obtained: CH₃F, 340 ± 70; CH₃CHF₂, 240 ± 50; CH₂FCl, 110 ± 25; CHFCl₂, 21 ± 4; CHCl₂CF₃, 14 ± 3; CHFClCF₃, 2.7 ± 0.6; CH₃CFCl₂, 2.4 ± 0.5; CHF₂Cl, 2.0 ± 0.4; CH₂FCF₃, 1.6 ± 0.3; CH₃CF₂Cl, 0.37 ± 0.08; and CHF₂CF₃, 0.24 ± 0.05. These Cl atom reaction rate constants are compared with literature data and with the corresponding OH radical reaction rate constants. © John Wiley & Sons, Inc.     

Rate constants for the gas-phase reactions of O3 with a series of carbonyls at 296 K

Rate constants for the gas-phase reactions of O₃ with the carbonyls acrolein, crotonaldehyde, methacrolein, methylvinylketone, 3-penten-2-one, 2-cyclohexen-1-one, acetaldehyde, and methylglyoxal have been determined at 296 ± 2 K. The rate constants ranged from <6 × 10^?21 cm³ molecule^?1 s^?1 for acetaldehyde to 2.13 × 10^?17 cm³ molecule^?1 s^?1 for 3-penten-2-one. The substituent effects of ? CHO and CH₃CO? groups on the rate constants are assessed and discussed, as are implications for the atmospheric chemistry of the natural hydrocarbon isoprene.     

The ion product of H2O,dissociation constants of H2CO3 and pitzer parameters in the system Na+/H+/OH−/HCO 3 − /CO 3 2- /ClO 4 − /H2O at 25°C

The ion product of water and the dissociation constants of carbonic acid have been determined in 0.1, 1.0, 3.0, and 5.0M NaClO₄ at 25°C. The ion product of water K _w ^' has been evaluated by emf measurements with a combined glass electrode in NaClO₄ solutions containing 0.001–0.1M HCLO₄ or NaOH. The product K _H ^' K _l ^' K ₂ ^' of the Henry constant for CO₂ and the dissociation constants for H₂CO₃ have been determined by titration of carbonate solutions equilibrated with pCO₂ =10^–3.52 atm, and K ₂ ^' has been evaluated by potentiometric titration and by measuring the H⁺ concentration at fixed HCO ₃ ^– and CO ₃ ^2- concentrations. The ion interaction (Pitzer) equations are applied to describe the constants K _w ^' , K ₂ ^' and K _H ^' H ₁ ^' K ₂ ^' as a function of the NaClO₄ concentration. The experimental data are used to evaluate the mixing parameters _{i/ClO 4} and _{i/ClO 4} ^-/Na⁺ fori = OH ^-,HCO ₃ ^- andCO ₃ ^2-     

The QCT calculation of the rate constants for the N(4S)+O2(X3Σ g ? ) →NO(X2Π)+O(3P) reaction

A quasi-classical trajectory (QCT) calculation with the fourth-order explicit symplectic algorithm for the N(⁴S) + O₂(X³Σ_g⁻) → NO(X²Π) + O(³P) reaction has been performed by employing the ground and first-excited potential energy surfaces (PESs). Since the translational temperature considered is up to 5000 K, the larger relative translational energy and the higher vibrational and rotational level of O₂ molecule have been taken into account. The affect of the relative translational energy, the vibrational and rotational level of O₂ molecule in the reaction cross-sections of the ground and first-excited PESs has been discussed in a extensive range. And we exhibit the dependence of microscopic rate constants on the vibrational and rotational level of O₂ molecule at T = 4000 K. The thermal rate constants at the translational temperature betweem 300 and 5000 K have been evaluated and the corresponding Arrhenius curve has been fitted for reaction (1). It is found by comparison that the thermal rate constants determined in this work have a better agreement with the experimental data and provide a more valid theoretical reference.     

The limiting dissociative mechanism for substitution at thed 6 centres molybdenum(O), iron(II), and cobalt(III): Kinetics of substitution at the pentacyano-4-Cyanopyridineferrate(II) anion and at 4-cyanopyridinemolybdenum(I) pentacarbonyl

Summary Rate constants are reported for reaction of the 4-cyanopyridine complexes [Fe(CN)₅(4CNpy)]^3– and [Mo(CO)₅(4CNpy)] with a variety of incoming ligands, in aqueous methanol (40 vol % MeOH) and in toluene respectively, at 298.2 K (ambient pressure). The dependence of rate constants on the nature and concentration of the incoming ligand is discussed in terms of the operation of the limiting dissociative,D, mechanism for substitution; the operation of this mechanism here, and in analogous pentacyanoferrate(II), pentacarbonylmolybdenum(I), and penta- and tetra-cyanocobaltate(III) complexes is reviewed. The effect of pressure on rate constants for replacement of 4-cyanopyridine in [Mo(CO)₅(4CNpy)], in toluene solution at 298.2 K, indicates an activation volume of +3 cm³ mol^–1.     

Kinetics of the gas-phase reactions of β-phellandrene with OH and NO3 radicals and O3 at 297 ± 2 K

Rate constants for the gas-phase reactions of the biogenically emitted monoterpene β-phellandrene with OH and NO₃ radicals and O₃ have been measured at 297 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained were (in cm³ molecule^?1 s^?1 units): for reaction with the OH radical, (1.68 ± 0.41) × 10^?10; for reaction with the NO₃ radical, (7.96 ± 2.82) × 10^?12; and for reaction with O₃, (4.77 ± 1.23) × 10^?17, where the error limits include the estimated uncertainties in the reference reaction rate constants. Using these rate constants, the lifetime of β-phellandrene in the lower troposphere due to reaction with these species is calculated to be in the range of ca. 1–8 h, with the OH radical reaction being expected to dominate over the O₃ reaction as a loss process for β-phellandrene during daylight hours.     

C_2(a~3П_u)自由基与含硫小分子反应的温度效应

运用脉冲激光光解-激光诱导荧光(PLP-LIF)的方法在298-673 K的温度范围内测量了C2(a3Пu)自由基与含硫小分子(H2S,SO2,CS2)气相反应的双分子反应速率常数.获得的速率常数可以用Arrhenius公式表达如下(单位:cm3·molecule-1·s-1):k(H2S)=(1.61±0.06)×10-12exp[-(180.91±15.73)/T],k(SO2)=(1.26±0.10)×10-15×exp[(2230.68±27.77)/T],k(CS2)=(1.17±0.02)×10-10exp[(253.31±7.69)/T];误差为2σ.由获得的双分子速率常数及所表现的正温度效应,认为C2(a3Пu)与H2S反应遵循抽氢反应机理;C2(a3Пu)与SO2反应是无能垒的过程,反应速率表现出强的负温度依赖关系;根据较大的双分子速率常数及其呈现的负温度效应我们认为,C2(a3Пu)与CS2反应遵循加成反应机理.     

Effects of ring strain on gas-phase rate constants. 3. NO3 radical reactions with cycloalkenes

Rate constants for the gas-phase reactions of NO₃ radicals with a series of cycloalkenes have been determined at 298 ± 2 K, using a relative rate technique. Using an equilibrium constant for the NO₂ + NO₃ ? N₂O₅ reactions of 3.4 × 10^?11 cm³ molecule^?1, the following rate constants (in units of 10^?13 cm³ molecule^?1 s^?1) were obtained: cyclopentene, 4.52 ± 0.52; cycloheptene, 4.71 ± 0.56; bicyclo[2.2.1]-2-heptene, 2.41 ± 0.28; bicyclo[2.2.2]-2-octene, 1.41 ± 0.17; bicyclo[2.2.1]-2,5-heptadiene, 9.92 ± 1.13; and 1,3,5-cycloheptatriene, 12.6 ± 2.9. When combined with previous literature rate constants for cyclohexene and 1,4-cyclohexadiene, these data show that the rate constants for the nonconjugated cycloalkenes studied depend to a first approximation on the number of double bonds and the degree and configuration of substitution per double bond. No obvious effects of ring strain energy on these NO₃ radical addition rate constants were observed. Our previous a priori predictive techniques for the alkenes and cycloalkenes can now be extended to strained cycloalkenes.     

Reactions of He+ and N+ ions with several molecules at 8 K

The rate constants for the reactions of He⁺ ions with N₂, O₂ and CO and N⁺ ions with O₂, CO and CH₄ have been measured at 8 K in a supersonic jet apparatus (CRESU). The reactions are all fast and the rate constants do not change in going from 300 K (88 K in the case of N⁺ + CO) to 8 K. This indicates that the existence of quadrupole moments and anisotropic polarizabilities of the linear neutrals do not contribute to a significant change in collision rate constant or reaction efficiency over this extreme temperature range.     

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.     

Flow reactor studies of methyl radical oxidation reactions in methane‐perturbed moist carbon monoxide oxidation at high pressure with model sensitivity analysis

New rate constant determinations for the reactions CH₃ + HO₂ → CH₃O + OH (1) CH₃ + HO₂ → CH₄ + O₂ (2) CH₃ + O₂ → CH₂O + OH (3) were made at 1000 K by fitting species profiles from high‐pressure flow reactor experiments on moist CO oxidation perturbed with methane. These reactions are important steps in the intermediate‐temperature burnout of hydrocarbon pollutants, especially at super‐atmospheric pressure. The experiments used in the fit were selected to minimize the uncertainty in the determinations. These uncertainties were estimated using model sensitivity coefficients, derived for time‐shifted flow reactor experiments, along with literature uncertainties for the unfitted rate constants. The experimental optimization procedure significantly reduced the uncertainties in each of these rate constants over the current literature values. The new rate constants and their uncertainties were determined to be, at 1000 K: k₁ = 1.48(10)¹³ cm³ mol⁻¹ s⁻¹ (UF = 2.24) k₂ = 3.16(10)¹² cm³ mol⁻¹ s⁻¹ (UF = 2.89) k₃ = 2.36(10)⁸ cm³ mol⁻¹ s⁻¹ (UF = 4.23) There are no direct and few indirect measurements of reactions ( 1 ) and ( 2 ) in the literature. There are few measurements of reaction ( 3 ) near 1000 K. These results therefore represent an important refinement to radical oxidation chemistry of significance to methane and higher alkane oxidation. The model sensitivity analysis used in the experimental design was also used to characterize the mechanistic dependence of the new rate constant values. Linear sensitivities of the fitted rate constants to the unfitted rate constants were given. The sensitivity analysis was used to show that the determinations above are primarily dependent on the rate constants chosen for the reactions CH₃ + CH₃ + M → C₂H₆ + M and CH₂O + HO₂ → HCO + H₂O₂. Uncertainties in the rate constants of these two reactions are the primary contributors to the uncertainty factors given above. Further reductions in the uncertainties of these kinetics would lead to significant reductions in the uncertainties in our determinations of k₁, k₂, and k₃. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 75–100, 2001     

Absolute Rate Constants for the Addition of Cyanomethyl (·CH2CN) and (tert-Butoxy)carbonylmethyl (·CH2CO2C(CH3)3) radicals to alkenes in solution

Absolute rate constants and their temperature dependence were determined by time-resolved electron spin resonance for the addition of the radicals ·CH₂CN and ·CH₂CO₂C(CH₃)₃ to a variety of mono- and 1,1-disubstituted and to selected 1,2- and trisubstituted alkenes in acetonitrile solution. To alkenes CH₂?CXY, ·CH₂CN adds at the unsubstituted C-atom with rate constants ranging from 3.3·10³ M ^?1S ^?1 (ethene) to 2.4·10⁶ M ^?1S ^?1 (1,1-diphenylethene) at 278 K, and the frequency factors are in the narrow range of log (A/M ^?1S ^?1) = 8.7 ± 0.3. ·CH₂CO₂C(CH₃)₃ shows a very similar reactivity with rate constants at 296 K ranging from 1.1·10⁴ M ^?1S ^?1 (ethene) to 10⁷ M ^?1S ^?1 (1,1-diphenylethene) and frequency factors log (A/M ^?1S ^?1) = 8.4 ± 0.1. For both radicals, the rate constants and the activation energies for addition to CH₂?CXY correlate well with the overall reaction enthalpy. In contrast to the expectation of an electro- or ambiphilic behavior, polar alkene-substituent effects are not clearly expressed, but some deviations from the enthalpy correlations point to a weak electrophilicity of the radicals. The rate constants for the addition to 1,2- and to trisubstituted alkenes reveal additional steric substituent effects. Self-termination rate data for the title radicals and spectral properties of their adducts to the alkenes are also given.     

Rate constants for the reactions of O3 and OH radicals with a series of alkynes

Rate constants for the reactions of O₃ and OH radicals with acetylene, propyne, and 1-butyne have been determined at room temperature. The rate constants obtained at 294 ± 2 K for the reactions of O₃ with acetylene, propyne, and 1-butyne were (7.8 ± 1.2) × 10^?21 cm³/molecule · s, (1.43 ± 0.15) × 10^?20 cm³/molecule · s, and (1.97 ± 0.26) × 10^?20 cm³/molecule · s, respectively. The rate constants at 298 ± 2 K and atmospheric pressure for the reactions with the OH radical, relative to a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10^?12 cm³/molecule · s, were determined to be (8.8 ± 1.4) × 10^?13 cm³/molecule · s, (6.21 ± 0.31) × 10^?12 cm³/molecule · s, and (8.25 ± 0.23) × 10^?12 cm³/molecule · s for acetylene, propyne, and 1-butyne, respectively. These data are discussed and compared with the available literature rate constants.     

Ab initio chemical kinetics for the NH2 + HNOx reactions,part III: Kinetics and mechanism for NH2 + HONO2

The kinetics and mechanism for the reaction of NH₂ with HONO₂ have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of this reaction has been computed by single‐point calculations at the CCSD(T)/6‐311+G(3df, 2p) level based on geometries optimized at the B3LYP/6‐311+G(3df, 2p) level. The reaction producing the primary products, NH₃ + NO₃, takes place via a precursor complex, H₂N…HONO₂ with an 8.4‐kcal/mol binding energy. The rate constants for major product channels in the temperature range 200–3000 K are predicted by variational transition state or variational Rice–Ramsperger–Kassel–Marcus theory. The results show that the reaction has a noticeable pressure dependence at T < 900 K. The total rate constants at 760 Torr Ar‐pressure can be represented by k_total = 1.71 × 10^?3 × T^?3.85 exp(?96/T) cm³ molecule^?1 s^?1 at T = 200–550 K, 5.11 × 10^?23 × T^+3.22 exp(70/T) cm³ molecule^?1 s^?1 at T = 550–3000 K. The branching ratios of primary channels at 760 Torr Ar‐pressure are predicted: k₁ producing NH₃ + NO₃ accounts for 1.00–0.99 in the temperature range of 200–3000 K and k₂ + k₃ producing H₂NO + HONO accounts for less than 0.01 when temperature is more than 2600 K. The reverse reaction, NH₃ + NO₃ → NH₂ + HONO₂ shows relatively weak pressure dependence at P < 100 Torr and T < 600 K due to its precursor complex, NH₃…O₃N with a lower binding energy of 1.8 kcal/mol. The predicted rate constants can be represented by k_?1 = 6.70 × 10^?24 × T^+3.58 exp(?850/T) cm³ molecule^?1 s^?1 at T = 200–3000 K and 760 Torr N₂ pressure, where the predicted rate at T = 298 K, 2.8 × 10^?16 cm³ molecule^?1 s^?1 is in good agreement with the experimental data. The NH₃ + NO₃ formation rate constant was found to be a factor of 4 smaller than that of the reaction OH + HONO₂ producing the H₂O + NO₃ because of the lower barrier for the transition state for the OH + HONO₂. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 69–78, 2010