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1.
Reactions of oxygen atoms with ethylene, propene, and 2-butene were studied at room temperature under discharge flow conditions by resonance fluorescence spectroscopy of O and H atoms at pressures of 0.08 to 12 torr. The measured total rate constants of these reactions are K = (7.8 ± 0.6)·10?13cm3s?1,K = (4.3 ± 0.4) ± 10?12 cm3 s?1, K = (1.4 ± 0.4) · 10?11 cm3 s?1. The branching ratios of H atom elimination channels were measured for reactions of O atoms with ethylene and propene. No H-atom elimination was found for the reaction of O-atoms with 2-butene. A redistribution of reaction O + C2 channels with pressure was found. A mechanism of the O + C2 reaction was proposed and the possibility of its application to other olefins is discussed. On the basis of mechanism the pressure dependence of the total rate constant for reaction O + C2 was predicted and experimentally confirmed in the pressure range 0.08–1.46 torr.  相似文献   

2.
Published experimental studies concerning the determination of rate constants for the reaction F + H2 → HF + H are reviewed critically and conclusions are presented as to the most accurate results available. Based on these results, the recommended Arrhenius expression for the temperature range 190–376 K is k = (1.1 ± 0.1) × 10−10 exp |-(450 ± 50)/T| cm3 molecule−1 s−1, and the recommended value for the rate constant at 298 K is k = (2.43 ± 0.15) × 10−11 cm3 molecule−1 s−1. The recommended Arrhenius expression for the reaction F + D2 → DF + D, for the same temperature range, based on the recommended expression for k and accurate results for the kinetic isotope effect k/k is k = (1.06 ± 0.12) × 10×10 exp |-(635 ± 55)/T|cm3 molecule−1 s−1, and the recommended value for 298 K is k = (1.25 ± 0.10) × 10−11 cm3 molecule−1 s−1. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 67–71, 1997.  相似文献   

3.
The kinetics of the oxidation of formate, oxalate, and malonate by |NiIII(L1)|2+ (where HL1 = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) were carried out over the regions pH 3.0–5.75, 2.80–5.50, and 2.50–7.58, respectively, at constant ionic strength and temperature 40°C. All the reactions are overall second-order with first-order on both the oxidant and reductant. A general rate law is given as - d/dt|NiIII(L1)2+| = kobs|NiIII(L1)2+| = (kd + nks |R|)|NiIII(L1)2+|, where kd is the auto-decomposition rate constant of the complex, ks is the electron transfer rate constant, n is the stoichiometric factor, and R is either formate, oxalate, or malonate. The reactivity of all the reacting species of the reductants in solution were evaluated choosing suitable pH regions. The reactivity orders are: kHCOOH > k; k > k > k, and k > k < k for the oxidation of formate, oxalate, and malonate, respectively, and these trends were explained considering the effect of hydrogen bonded adduct formation and thermodynamic potential. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 225–230, 1997.  相似文献   

4.
The results of comprehensive equilibrium and kinetic studies of the iron(III)–sulfate system in aqueous solutions at I = 1.0 M (NaClO4), in the concentration ranges of T = 0.15–0.3 mM, and at pH 0.7–2.5 are presented. The iron(III)–containing species detected are FeOH2+ (=FeH?1), (FeOH) (=Fe2H?2), FeSO, and Fe(SO4) with formation constants of log β = ?2.84, log β = ?2.88, log β = 2.32, and log β = 3.83. The formation rate constants of the stepwise formation of the sulfate complexes are k1a = 4.4 × 103 M?1 s?1 for the ${\rm Fe}^{3+} + {\rm SO}_4^{2-}\,\stackrel{k_{1a}}{\rightleftharpoons}\, {\rm FeSO}_4^+The results of comprehensive equilibrium and kinetic studies of the iron(III)–sulfate system in aqueous solutions at I = 1.0 M (NaClO4), in the concentration ranges of T = 0.15–0.3 mM, and at pH 0.7–2.5 are presented. The iron(III)–containing species detected are FeOH2+ (=FeH?1), (FeOH) (=Fe2H?2), FeSO, and Fe(SO4) with formation constants of log β = ?2.84, log β = ?2.88, log β = 2.32, and log β = 3.83. The formation rate constants of the stepwise formation of the sulfate complexes are k1a = 4.4 × 103 M?1 s?1 for the ${\rm Fe}^{3+} + {\rm SO}_4^{2-}\,\stackrel{k_{1a}}{\rightleftharpoons}\, {\rm FeSO}_4^+$ step and k2 = 1.1 × 103 M?1 s?1 for the ${\rm FeSO}_4^+ + {\rm SO}_4^{2-} \stackrel{k_2}{\rightleftharpoons}\, {\rm Fe}({\rm SO}_4)_2^-$ step. The mono‐sulfate complex is also formed in the ${\rm Fe}({\rm OH})^{2+} + {\rm SO}_4^{2-} \stackrel{k_{1b}}{\longrightarrow} {\rm FeSO}_4^+$ reaction with the k1b = 2.7 × 105 M?1 s?1 rate constant. The most surprising result is, however, that the 2 FeSO? Fe3+ + Fe(SO4) equilibrium is established well before the system as a whole reaches its equilibrium state, and the main path of the formation of Fe(SO4) is the above fast (on the stopped flow scale) equilibrium process. The use and advantages of our recently elaborated programs for the evaluation of equilibrium and kinetic experiments are briefly outlined. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 114–124, 2008  相似文献   

5.
The mechanism of the photolysis of formaldehyde was studied in experiments at 3130 Å and in the pressure range of 1–12 torr at 25°C. The experiments were designed to establish the quantum yields of the primary decomposition steps (1) and (2), CH2O + hν → H + HCO (1): CH2O + hν → H2 + CO (2), through the effects of added isobutene, trimethylsilane, and nitric oxide on ΦCO and Φ. The ratio ΦCO/Φ was found to be 1.01 ± 0.09(2σ) and (Φ + ΦCO)/2 = 1.10 ± 0.08 over the range of pressures and a 12-fold change in incident light intensity. Isobutene and nitric oxide additions reduced Φ to about the same limiting value, 0.32 ± 0.03 and 0.34 ± 0.04, respectively, but these added gases differed in their effects on ΦCO. With isobutene addition ΦCO/Φ reached a limiting value of 2.3; with NO addition ΦCO exceeded unity. The addition of small amounts of Me3SiH reduced Φ to 1.02 ± 0.08 and lowered ΦCO to 0.7. These findings were rationalized in terms of a mechanism in which the “nonscavengeable,” molecular hydrogen is formed in reaction (2) with ?2 = 0.32 ± 0.03, while the “free radical” hydrogen is formed in reaction (1) with ?1 = 0.68 ± 0.03. In the pure formaldehyde system these reactions are followed by (3)–(5): H + CH2O → H2 + HCO (3); 2HCO → CH2O + CO (4); 2HCO → H2 + 2CO (5). The data suggest k4/k5 ? 5.8. Isobutene reduced Φ by the reaction H + iso-C4H8 → C4H9 (20), and the results give k20/k3 ? 43 ± 4, in good agreement with the ratio of the reported values of the individual constants k3 and k20.  相似文献   

6.
Hexafluoroacetone (HFA) and O2 were photolyzed at 147.0 nm to investigate their use in chemical actinometry. The products, CO for the former and O3 in the latter case, were monitored. For accurate comparison, both of these substances were irradiated by a single light source with two identical reaction cells at 180° to each other. The light intensities I were measured under the same integrated as well as instantaneous photon flux based on ? and ?CO (quantum yield) as 2 and 1, respectively. Optimum conditions for maximum product yield were 5.0 torr HFA pressure and an O2 flow rate of 200 ml/min at 1 atm pressure for a 20-minute photolysis period. For light intensity variations between 1.09 × 1014 and 2.10 × 1015 photons absorbed/sec, the ratio I/IHFA was found to be unity. Calibration with the commonly used N2O actinometer for a ? value of 1.41 showed that I/IHFA and I/I are unity. Both HFA and O2 are suitable chemical actinometers at 147.0 nm with ?CO and ? of 1 and 2, respectively. The light intensity determination in the first case involves the measurement of only one product which is noncondensible at 77°K, whereas wet analysis for O3, the only product, in the second actinometer is necessary. Both of these determinations are quite simple and are preferable over product analysis in N2O actiometry, wherein N2 separation from other noncondensibles at 77°K is required.  相似文献   

7.
The kinetics of the “a” and “b” band emissions arising from the 1Σ ← 3Ou and 1Σ ← 3lu transitions of the diatomic mercury molecule at λmax ~ 4850 Å and 3350 Å, respectively, have been studied at low concentrations of mercury in the presence of N2, C2H6, C3H8, and N2O. Rate constant values have been obtained for the following reactions of the excimer molecule: Hg2(3lu) + N2 → Hg2(3Ou) + N2 and Hg2(3Ou) + RH → Hg2(1Σ) + RH, where RH = C2H6 or C3H8. From a consideration of the detailed kinetics of band emissions, it was also possible to derive rate constants for the quenching reactions of Hg(3P0) atoms. These values are in reasonable agreement with those obtained previously from monitoring atom concentrations directly by 4047 Å absorbiometry.  相似文献   

8.
The kinetics of the acqueous-phase reactions of the free radicals ·OH, ·Cl, and SO· with the halogenated acetates, CH2FCOO?, CHF2COO?, CF3COO?, and with CH2ClCOO?, CHCl2COO?, CCl3COO? were investigated. Generally, the reactivity decreases with increasing halogen substitution and is in the order k(·OH) > k(SO·) > k(·Cl), but there is no general relation between the effect on reactivity of chlorine and fluorine substitution. © 1995 John Wiley & Sons, Inc.  相似文献   

9.
The kinetic isotope effects in the reaction of methane (CH4) with Cl atoms are studied in a relative rate experiment at 298 ± 2 K and 1013 ± 10 mbar. The reaction rates of 13CH4, 12CH3D, 12CH2D2, 12CHD3, and 12CD4 with Cl radicals are measured relative to 12CH4 in a smog chamber using long path FTIR detection. The experimental data are analyzed with a nonlinear least squares spectral fitting method using measured high‐resolution spectra as well as cross sections from the HITRAN database. The relative reaction rates of 12CH4, 13CH4, 12CH3D, 12CH2D2, 12CHD3, and 12CD4 with Cl are determined as k/k = 1.06 ± 0.01, k/k = 1.47 ± 0.03, k/k = 2.45 ± 0.05, k/k = 4.7 ± 0.1, k/k = 14.7 ± 0.3. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 110–118, 2005  相似文献   

10.
The activation energy parameters for the reaction of PdX (X=Cl?, Br?) in aqueous halide acid solution with thiourea (tu) and selenourea (seu) have been determined. High rates of reaction parallel low enthalpies and appreciable negative entropy of activation. The rate law in each case simplifies to kobs=k[L] where L=tu or seu, and only ligand-dependent rate constants are observed at 25°C. The ligand-dependent rate constants for the first identifiable step in the PdCl + X system is (9.1±0.1) × 103 M?1 sec?1 and (4.5±0.1) × 104 M?1 sec?1 for X=tu and seu, respectively, while for the PdBr + X system it is (2.0±0.1) × 104 M?1 sec?1 and (9.0±0.1) × 104 M?1 sec?1 for X=tu and seu, respectively.  相似文献   

11.
Ultraviolet absorption spectra have been characterized for the acetyl-h3 and acetyl-d3 radicals, which were generated by the flash photolysis of the corresponding acetones. The spectra are broad and intense, with values of the extinction coefficient at the respective maxima estimated as: ?CH3CO(215) = (1.0 ± 0.1) × 104 L/mol·cm and ?CD3CO(207.5) = (1.0 ± 0.05) × 104 L/mol·cm. Rate constants for the reactions of mutual interaction were estimated as: k = 3.5 × 1010 L/mol·s and k = 3.4 × 1010 L/mol·s. Rate constants for the reactions of cross interaction were estimated as: k = 8.6 × 1010 L/mol·s and k = 5.2 × 1010 L/mol·s. The related values of the cross interaction ratios k/(kk)1/2 = 2.6 and k/(kk)1/2 = 1.6 do not differ significantly from the statistical value of 2. The participation of the radical displacement reactions was estimated in terms of the fractions k/k = 0.38 and k/k = 0.47. Corroborative spectra were obtained from the flash photolysis of methyl ethyl ketone and biacetyl, and the relative rates of the competing primary processes were estimated from the relative peak heights of the acetyl and methyl radicals in each system.  相似文献   

12.
The substituted thiourea, 4‐methyl‐3‐thiosemicarbazide, was oxidized by iodate in acidic medium. In high acid concentrations and in stoichiometric excess of iodate, the reaction displays an induction period followed by the formation of aqueous iodine. In stoichiometric excess of methylthiosemicarbazide and high acid concentration, the reaction shows a transient formation of aqueous iodine. The stoichiometry of the reaction is: 4IO + 3CH3NHC(S)NHNH2 + 3H2O → 4I + 3SO + 3CH3NHC(O)NHNH2 + 6H+ (A). Iodine formation is due to the Dushman reaction that produces iodine from iodide formed from the reduction of iodate: IO + 5I + 6H+ → 3I2(aq) + 3H2O (B). Transient iodine formation is due to the efficient acid catalysis of the Dushman reaction. The iodine produced in process B is consumed by the methylthiosemicarbazide substrate. The direct reaction of iodine and methylthiosemicarbazide was also studied. It has a stoichiometry of 4I2(aq) + CH3NHC(S)NHNH2 + 5H2O → 8I + SO + CH3NHC(O)NHNH2 + 10H+ (C). The reaction exhibits autoinhibition by iodide and acid. Inhibition by I is due to the formation of the triiodide species, I, and inhibition by acid is due to the protonation of the sulfur center that deactivates it to further electrophilic attack. In excess iodate conditions, the stoichiometry of the reaction is 8IO + 5CH3NHC(S)NHNH2 + H2O → 4I2 + 5SO + 5CH3NHC(O)NHNH2 + 2H+ (D) that is a linear combination of processes A and B. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 193–203, 2000  相似文献   

13.
Kinetics of the complex formation of chromium(III) with alanine in aqueous medium has been studied at 45, 50, and 55°C, pH 3.3–4.4, and μ = 1 M (KNO3). Under pseudo first-order conditions the observed rate constant (kobs) was found to follow the rate equation: Values of the rate parameters (kan, k, KIP, and K) were calculated. Activation parameters for anation rate constants, ΔH(kan) = 25 ± 1 kJ mol?1, ΔH(k) = 91 ± 3 kJ mol?1, and ΔS(kan) = ?244 ± 3 JK?1 mol?1, ΔS(k) = ?30 ± 10 JK?1 mol?1 are indicative of an (Ia) mechanism for kan and (Id) mechanism for k routes (‥substrate Cr(H2O) is involved in the k route whereas Cr(H2O)5OH2+ is involved in k′ route). Thermodynamic parameters for ion-pair formation constants are found to be ΔH°(KIP) = 12 ± 1 kJ mol?1, ΔH°(K) = ?13 ± 3 kJ mol?1 and ΔS°(KIP) = 47 ± 2 JK?1 mol?1, and ΔS°(K) = 20 ± 9 JK?1 mol?1.  相似文献   

14.
Kinetic solvent isotope effects (KSIE) were measured for the hydrolyses of acetals of benzaldehydes in aqueous solutions covering the pH (pD) range of 1–6. For p-methoxybenzaldehyde diethyl acetal, k/k = 1.8–3.1, depending on the procedure used to calculate the KSIE and on the pH (pD) range used as the basis for k(k). It is shown that this variation is an experimental artifact, and is a characteristic of KSIE measurements in general. It is recommended that k be calculated from a least-squares fit of data to the equation kobs = k[L+], and that the KSIE be reported as k/k. The limitation remains, however, that the KSIE measured for a variety of substances over quite different pH (pD) ranges may not be comparable to more than ?20%. The source of these observations is discussed in terms of small changes in the activity coefficient ratios (a specific salt effect), including the solvent isotope effect on the activity coefficient ratio [eq. (3)].  相似文献   

15.
The extinction coefficients and the decay kinetics of I and (SCN) have been characterized over the 15–90°C-temperature range. The extinction coefficients of I at 385 and 725 nm were determined to be 10,000 and 2560M?1 cm?1, respectively, based on the extinction coefficient of (SCN) at 475 nm being equal to 7600M?1 cm?1. At these three wavelengths, all extinction coefficients were constant over the temperature range studied. The rate of decay of both I and (SCN) was found to be a function of I? and SCN? concentration, respectively, as well as temperature.  相似文献   

16.
The title reaction, which is spin‐forbidden for N2(X1∑) + NO(X2Π) production, has been studied from 960 to 1130 K in a high‐temperature photochemistry reactor. No reaction could be observed, indicating k < 1 × 10?15 cm3 molecule?1 s?1. It is concluded that there is no significant contribution from the spin‐allowed exothermic path leading to N2(X1∑) + NO(a4Π). © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 387–389, 2001  相似文献   

17.
Rate constants for the reaction O(3P) + SO2 + M have been determined over the temperature range of 299°–440°K, using a flash photolysis–NO2 chemiluminescence technique. For M?Ar, the Arrhenius expression was obtained. At room temperature k2Ar = (1.05 ± 0.21) × 10?33 cm6/molec2·sec. In addition, the rate constants k2 = (1.37 + 0.27) × 10?33 cm6/molec2·sec, k2 = (9.5 ± 3.0) ± 10?33 cm6/molec2·sec, k3 = (1.1 ± 0.2) ± 10?31 cm6/molec2·sec, and k3 = (2.6 ? 0.9) ± 10?31 cm6/molec2·sec were obtained at room temperature where k3M is the rate constant for the reaction O + NO + M → NO2 + M. The rate data are compared and discussed with literature values.  相似文献   

18.
The hexacyanoferrate(III)-thallium(I) reaction in aqueous acetic acid containing large concentrations of hydrochloric acid is considerably accelerated both by hydrogen and chloride ions as well as increasing acetic acid in the medium. The experimental results obey the rate law (1) where β1 to β6 are the cumulative stability constants of the species TlCl, TlCl, TlCl, HFe(CN), H2Fe(CN) and H3Fe(CN)6 respectively and ka and kb are the rate constants associated with the mono- and di-protonated oxidant species. The main active species are H2Fe(CN) and TlCl.  相似文献   

19.
The kinetics of the gas-phase thermal reaction between CF2(OF)2 and CO has been studied in a static system at temperatures ranging between 110 and 140°C. The only reaction products were CF2O and CO2, giving the following stoichiometry: The reaction is homogeneous. The rate is strictly second order in CF2(OF)2 and CO, and is not affected by the total pressure or by the presence of reaction products. Oxygen promotes a sensitized oxidation of CO and inhibits the formation of CF2O. The experimental results in the absence of oxygen can be explained by a chain mechanism similar to that proposed for the reaction between F2O and CO with an overall rate constant of From the experimental data obtained on the oxygen-inhibited reaction, the rate constant for the primary process can be calculated: The chain length v = 2.5 is independent of the temperature. Taking for collision diameters σ = 6 Å and σCO = 3.74 Å, a value α = 5.3 × 10?3 for the steric factor is obtained.  相似文献   

20.
Studies of the reaction of Br + propylene to produce HBr and allyl radical were made using VLPR (Very Low Pressure Reactor) over the range 263–363 K. Apparent bimolecular rate constants k were found to vary in an inverse manner with the initial concentration of bromine atoms introduced into the reactor. Plots of k against [Br] give straight lines whose intercepts were taken to be the true bimolecular, metathesis rate constant k1. The reaction scheme is where k2 ? k1 and k?1 [HBr] is negligibly small under our conditions. Arrhenius parameters for k1 were assigned for linear and bent transition states and shown to give excellent fits to the observed intercepts. where θ = 2.303 RT (kcal mol?1). The dependence of k on [Br] is accounted for in terms of the reactivity of Br* (2P1/2) produced in the microwave discharge. The activation energy for the metathesis reaction of Br* with propylene is shown to be very small.  相似文献   

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