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1.
Flash photolysis of NO coupled with time resolved detection of O via resonance fluorescence has been used to obtain rate constants for the reaction O + NO + N2 → NO2 + N2 at temperatures from 217 to 500 K. The measured rate constants obey the Arrhenius equation k = (15.5 ± 2.0) × 10?33 exp(1160 ± 70)/1.987 T] cm6 molecule?2 s?1. An equally acceptable equation describing the temperature dependence of k is k = 3.80 × 10?27/T1.82 cm6 molecule?2 s?1. These results are discussed and compared with previous work.  相似文献   

2.
The rate coefficients of the reactions of NCO radicals with NO and NO2: (1) NCO + NO → products (293–836 K) and : (2) NCO + NO2 → products (294–774 K) were measured by means of laser photolysis and laser induced fluorescence technique in the indicated temperature ranges. NCO radicals were produced from the reaction of CN, from photodissociation of ICN or BrCN, with O2. The concentration of NCO was monitored with a dye laser set at 414.95 nm. We determined k1 = 1.73 × 10?5 T?2.01 exp(?470/T) cm3 molecule?1 s?1 that agrees with published results at room temperature and confirms the temperature dependence of an early report. A non-Arrhenius negative temperature dependence of k2 was observed in this work that agrees satisfactorily with results for a shock tube18 near 1250 K. We obtained k2 = 6.4 × 10?10 T?0.646 exp(164/T) cm3 molecule?1 s?1 for 1250 K ≥ T ≥ 294 K by combining data of these two measurements. Our result at 294 K and the temperature dependence disagree with results of two previous investigations. © 1995 John Wiley & Sons, Inc.  相似文献   

3.
The reflected shock tube technique with multipass absorption spectrometric detection of OH‐radicals at 308 nm, corresponding to a total path length of 1.749 m, has been used to study the reaction H2O + M → H + OH + M between 2196 and 2792 K using 0.3, 0.5, and 1% H2O, diluted in Kr. As a result of the increased sensitivity for OH‐radical detection, the existing database for this reaction could be extended downward by ~500 K. Combining the present work with that of Homer and Hurle, the composite rate expression for water dissociation in either Ar or Kr bath gas is k1,Ar(or Kr) = (2.43 ± 0.57) × 10?10 exp(?47117 ± 633 K/T) cm3 molecule?1 s?1 over the T‐range of 2196–3290 K. Applying the Troe factorization method to data for both forward and reverse reactions, the rate behavior could be expressed to within <±18% over the T‐range, 300–3400 K, by the three‐parameter expression k1,Ar = 1.007 × 104 T?3.322 exp(?60782 K/T) cm3 molecule?1 s?1 A large enhancement due to H2O with H2O collisional activation has been noted previously, and both absolute and relative data have been considered allowing us to suggest k1, H2 O = 1.671 × 102 T?2.440 exp(?60475 K/T) cm3 molecule?1 s?1 for the rate constants with H2O bath gas over the T‐range, 300–3400 K. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 211–219, 2006  相似文献   

4.
Flash photolysis of CH3CHO and H2CO in the presence of NO has been investigated by the intracavity laser spectroscopy technique. The decay of HNO formed by the reaction HCO + NO → HNO + CO was studied at NO pressures of 6.8–380 torr. At low NO pressure HNO was found to decay by the reaction HNO + HNO → N2O + H2O. The rate constant of this reaction was determined to be k1 = (1.5 ± 0.8) × 10?15 cm3/s. At high NO pressure the reaction HNO + NO → products was more important, and its rate constant was measured to be k2 = (5 ± 1.5) × 10?19 cm3/s. NO2 was detected as one of the products of this reaction. Alternative mechanisms for this reaction are discussed.  相似文献   

5.
The rate constants of the reactions of ethoxy (C2H5O), i‐propoxy (i‐C3H7O) and n‐propoxy (n‐C3H7O) radicals with O2 and NO have been measured as a function of temperature. Radicals have been generated by laser photolysis from the appropriate alkyl nitrite and have been detected by laser‐induced fluorescence. The following Arrhenius expressions have been determined: (R1) C2H5O + O2 → products k1 = (2.4 ± 0.9) × 10−14 exp(−2.7 ± 1.0 kJmol−1/RT) cm3 s−1 295K < T < 354K p = 100 Torr (R2) i‐C3H7O + O2 → products k2 = (1.6 ± 0.2) × 10−14 exp(−2.2 ± 0.2 kJmol−1/RT) cm3 s−1 288K < T < 364K p = 50–200 Torr (R3) n‐C3H7O + O2 → products k3 = (2.5 ± 0.5) × 10−14 exp(−2.0 ± 0.5 kJmol−1/RT) cm3 s−1 289K < T < 381K p = 30–100 Torr (R4) C2H5O + NO → products k4 = (2.0 ± 0.7) × 10−11 exp(0.6 ± 0.4 kJmol−1/RT) cm3 s−1 286K < T < 388K p = 30–500 Torr (R5) i‐C3H7O + NO → products k5 = (8.9 ± 0.2) × 10−12 exp(3.3 ± 0.5 kJmol−1/RT) cm3 s−1 286K < T < 389K p = 30–500 Torr (R6) n‐C3H7O + NO → products k6 = (1.2 ± 0.2) × 10−11 exp(2.9 ± 0.4 kJmol−1/RT) cm3s−1 289K < T < 380K p = 30–100 Torr All reactions have been found independent of total pressure between 30 and 500 Torr within the experimental error. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 860–866, 1999  相似文献   

6.
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] · 1017.1 exp(?42(kcal/mol)/RT) cm3/ mol sec in the range 900 < T < 1400 K and limiting high pressure rate constants of k = 1016.25 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.  相似文献   

7.
The rate constant for the reaction of ground-state oxygen atoms with methanol has been determined between 297 and 544 K by a phase-shift technique using mercury photosensitized decomposition of N2O to generate oxygen atoms. The relative oxygen atom concentration was monitored by the chemiluminescence from the reaction of oxygen atoms with nitric oxide. The results are accommodated by the Arrhenius expression k1 = (9.79 ± 2.71) × 1012 exp[(?2267 ± 111)/T]cm3/mol·s, where the indicated uncertainties are 95% confidence limits for 10 degrees of freedom. As an incidental part of this work, the third-body efficiency of CH3OH relative to N2O for the reaction O + NO + M → NO2 + M (M = CH3OH) was determined to be 3.1 at 298 K.  相似文献   

8.
We have conducted flow reactor experiments for NO formation from N2/O2 mixtures at high temperatures and atmospheric pressure, controlling accurately temperature and reaction time. Under these conditions, atomic oxygen equilibrates rapidly with O2. The experimental results were interpreted by a detailed chemical model to determine the rate constant for the reaction N2 + O ? NO + N (R1). We obtain k1 = 1.4 × 1014 exp(?38,300/T) cm3 mol?1 s?1 at 1700–1800 K, with an error limit of ±30%. This value is 25% below the recommendation of Baulch et al. for k1, while it corresponds to a value k1b of the reverse reaction 25% above the Baulch et al. evaluation. Combination of our results with literature values leads to a recommended rate constant for k1b of 9.4 × 1012 T0.14 cm3 mol?1 s?1 over 250–3000 K. This value, which reconciles the differences between the forward and reverse rate constant, is recommended for use in kinetic modeling.  相似文献   

9.
High-temperature (>1000°K) pyrolysis of acetaldehyde (~1% in an atmosphere of pure nitrogen) was examined in a turbulent flow reactor which permits accurate determination of the spatial distribution of the stable species. Results show that the products in order of decreasing importance are CO, CH4, H2, C2H6, and C2H4. Rates of formation were consistent with the Rice–Herzfeld mechanism by including reactions to explain C2H4 formation and the possible presence of ketene. A steady-state treatment of the complete mechanism indicates that the overall reaction order decreases from \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{3}{2} $\end{document} to 1, which is supported by the new experimental data. Using earlier low-temperature results, the rate constant for the reaction CH3CHO → CH3 + CHO (1) was found as k1=1015.85±0.21 exp (?81,775±1000/RT) sec?1. Also, data for the ratio of rate constants for reactions CH3CHO + CH3 → CH4 + CH3CO (4) and 2CH3 → C2H6(6) were fitted to the empirical expression k4/k61/2=10?13.89±0.03T6.1 exp(?1720±70/RT) (cm3/mole·sec)1/2 and causes for the curvature are discussed. The noncatalytic effect of oxygen on acetaldehyde pyrolysis at high temperature is explained.  相似文献   

10.
The bimolecular reactions in the title were measured behind shock waves by monitoring the O-atom production in COS? O2? Ar and CS2? O2? Ar mixtures over the temperature range between 1400 and 2200 K. A value of the rate constant for S + O2 → SO + O was evaluated to be (3.8 ± 0.7) × 1012 cm3 mol?1 s?1 between 1900 and 2200 K. This was connected with the data at lower temperatures to give an expression k2 = 1010.85 T0.52 cm3 mol?1 s?1 between 250 and 2200 K. An expression of the rate constant for CS2 + O2 → CS + SO2 was obtained to be k21 = 1012.0 exp(?32 kcal mol?1/RT) cm3 mol?1 s?1 with an error factor of 2 between 1500 and 2100 K.  相似文献   

11.
Recent experimental results on the thermal decomposition of N2O5 in N2 are evaluated in terms of unimolecular rate theory. A theoretically consistent set of fall-off curves is constructed which allows to identify experimental errors or misinterpretations. Limiting rate constants k0 = [N2] 2.2 × 10?3 (T/300)?4.4 exp(?11,080/T) cm3/molec·s over the range of 220–300 K, k = 9.7 × 1014 (T/300)+0.1 exp(?11,080/T) s?1 over the range of 220–300 K, and broadening factors of the fall-off curve Fcent = exp(-T/250) + exp(?1050/T) over the range of 220–520 K have been derived. NO2 + NO3 recombination rate constants over the range of 200–300 K are krec,0 = [N2] 3.7 × 10?30 (T/300)?4.1 cm6/molec2·s and krec,∞ = 1.6 × 10?12 (T/300)+0.2 cm3/molec·s.  相似文献   

12.
A phase-shift method has been used to determine the rate constant for the reaction of ground state oxygen atoms with HCl over the temperature range of 330–600 K. Oxygen atoms were generated by modulated mercury photosensitized decomposition of N2O, and monitored by the chemiluminescence from their reaction with NO. After correction for diffusion of oxygen atoms from the viewing zone, the rate constants can be represented by the Arrhenius equation k1 = (3.06 ± 1.43) × 1012 exp[(?3160 ± 184)/T] cm3/mol·s. The indicated uncertainties are 95% confidence limits for 15 degrees of freedom. Also, the third-body efficiency of HCl relative to N2O in the reaction O + NO + M ← NO2 + M was determined to be 1.9 ± 0.2 over the temperature range of 298–360 K.  相似文献   

13.
The decomposition of C2H6 in Ar was studied by laser-absorption and laser-schlieren measurements of the reaction rate behind incident shock waves with 1300 < T < 2500°K and 1.1 < ρ < 4.4 × 10?6 mol/cm3. The experimental profiles were parameterized by suitable measures of reaction progress. Computer simulations using a 14-reaction mechanism were used to compare assumptions about rate constant expressions with the experimental parameters and to investigate the sensitivity of computed parameters to these assumptions. A rate constant expression k(cm3/mol˙sec) = 2 × 10111 T?25.26 exp(?80 320/T) was found for the primary dissociation step C2H6 + M ? CH3 + CH3 + M under the conditions studied; no difference in rate was discernable between M ? Ar and M ? C2H6. Rate constant expressions found to be suitable for the remaining reactions of the mechanism, to some of which the computed parameters were sensitive, were in accord with previous proposals. Our results and results from earlier investigations of the primary decomposition reaction, in both forward and reverse directions, were extrapolated, using RRK methods, to obtain low-pressure limiting rate constants and found to be concordant.  相似文献   

14.
The consumption of nitric oxide in the shock-heated nitric oxide, hydrogen, and argon system had been studied and modeled as the chain-branching process containing the reaction H + NO ? N + OH (k3) as a slow-branching step. Through the computer simulation method the authors clarified the role of the initiation reaction H2 + NO ? HNO + H (k1) in the system and obtained the rate constants of k1 and k3 as k1 = 1013.5±0.15 exp (?55.2 kcal/RT) and k3 = 1013.7±0.15 exp (?48.7 kcal/RT) (cm3/mole·sec), respectively. k1 was one order larger than the value obtained in the flame experiment by Halstead and Jenkins.  相似文献   

15.
Using the relative kinetic method, rate coefficients have been determined for the gas‐phase reactions of chlorine atoms with propane, n‐butane, and isobutane at total pressure of 100 Torr and the temperature range of 295–469 K. The Cl2 photolysis (λ = 420 nm) was used to generate Cl atoms in the presence of ethane as the reference compound. The experiments have been carried out using GC product analysis and the following rate constant expressions (in cm3 molecule?1 s?1) have been derived: (7.4 ± 0.2) × 10?11 exp [‐(70 ± 11)/ T], Cl + C3H8 → HCl + CH3CH2CH2; (5.1 ± 0.5) × 10?11 exp [(104 ± 32)/ T], Cl + C3H8 → HCl + CH3CHCH3; (7.3 ± 0.2) × 10?11 exp[?(68 ± 10)/ T], Cl + n‐C4H10 → HCl + CH3 CH2CH2CH2; (9.9 ± 2.2) × 10?11 exp[(106 ± 75)/ T], Cl + n‐C4H10 → HCl + CH3CH2CHCH3; (13.0 ± 1.8) × 10?11 exp[?(104 ± 50)/ T], Cl + i‐C4H10 → HCl + CH3CHCH3CH2; (2.9 ± 0.5) × 10?11 exp[(155 ± 58)/ T], Cl + i‐C4H10 → HCl + CH3CCH3CH3 (all error bars are ± 2σ precision). These studies provide a set of reaction rate constants allowing to determine the contribution of competing hydrogen abstractions from primary, secondary, or tertiary carbon atom in alkane molecule. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 651–658, 2002  相似文献   

16.
Relative rate techniques were used to study the title reactions in 930–1200 mbar of N2 diluent. The reaction rate coefficients measured in the present work are summarized by the expressions k(Cl + CH2F2) = 1.19 × 10?17 T2 exp(?1023/T) cm3 molecule?1 s?1 (253–553 K), k(Cl + CH3CCl3) = 2.41 × 10?12 exp(?1630/T) cm3 molecule?1 s?1 (253–313 K), and k(Cl + CF3CFH2) = 1.27 × 10?12 exp(?2019/T) cm3 molecule?1 s?1 (253–313 K). Results are discussed with respect to the literature data. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 401–406, 2009  相似文献   

17.
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 ktotal = 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  相似文献   

18.
The reaction of Cl atoms with a series of C2–C5 unsaturated hydrocarbons has been investigated at atmospheric pressure of 760 Torr over the temperature range 283–323 K in air and N2 diluents. The decay of the hydrocarbons was followed using a gas chromatograph with a flame ionization detector (GC‐FID), and the kinetic constants were determined using a relative rate technique with n‐hexane as a reference compound. The Cl atoms were generated by UV photolysis (λ ≥ 300 nm) of Cl2 molecules. The following absolute rate constants (in units of 10−11 cm3 molecule−1 s−1, with errors representing ±2σ) for the reaction at 295 ± 2 K have been derived from the relative rate constants combined to the value 34.5 × 10−11 cm3 molecule−1 s−1 for the Cl + n‐hexane reaction: ethene (9.3 ± 0.6), propyne (22.1 ± 0.3), propene (27.6 ± 0.6), 1‐butene (35.2 ± 0.7), and 1‐pentene (48.3 ± 0.8). The temperature dependence of the reactions can be expressed as simple Arrhenius expressions (in units of 10−11 cm3 molecule−1 s−1): kethene = (0.39 ± 0.22) × 10−11 exp{(226 ± 42)/T}, kpropyne = (4.1 ± 2.5) × 10−11 exp{(118 ± 45)/T}, kpropene = (1.6 ± 1.8) × 10−11 exp{(203 ± 79)/T}, k1‐butene = (1.1 ± 1.3) × 10−11 exp{(245 ± 90)/T}, and k1‐pentene = (4.0 ± 2.2) × 10−11 exp{(423 ± 68)/T}. The applicability of our results to tropospheric chemistry is discussed. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 478–484, 2000  相似文献   

19.
Reactions of ozone with simple olefins have been studied between 6 and 800 mtorr total pressure in a 220-m3 reactor. Rate constants for the removal of ozone by an excess of olefin in the presence of 150 mtorr oxygen were determined over the temperature range 280 to 360° K by continuous optical absorption measurements at 2537 Å. The technique was tested by measuring the rate constants k1 and k2 of the reactions (1) NO + O3 → NO2 + O2 and (2) NO2 + O3 rarr; NO3 + O2 which are known from the literature. The results for NO, NO2, C2H4, C3H6, 2-butene (mixture of the isomers), 1,3→butadiene, isobutene, and 1,1 -difluoro-ethylene are 1.7 × 10?1 4 (290°K), 3.24 × 10?17 (289°K), 1.2 × 10?1 4 exp (–4.95 ± 0.20/RT), 1.1 × 10?1 4 exp (–3.91 ± 0.20/RT), 0.94 × 10?1 4 exp ( –2.28 ± 0.15/RT), 5.45 ± 10?1 4 exp ( –5.33 ± 0.20/RT), 1.8 ×10?17 (283°K), and 8 × 10?20 cm3/molecule ·s(290°K). Productformation from the ozone–propylene reaction was studied by a mass spectrometric technique. The stoichiometry of the reaction is near unity in the presence of molecular oxygen.  相似文献   

20.
We have used the single‐pulse shock tube technique with postshock GC/MS product analysis to investigate the mechanism and kinetics of the unimolecular decomposition of isopropanol, a potential biofuel, and of its reaction with H atoms at 918‐1212 K and 183‐484 kPa. Experiments employed dilute mixtures in argon of isopropanol, a radical scavenger, and, for H‐atom studies, two different thermal precursors of H. Without an added H source, isopropanol decomposes in our studies predominantly by molecular dehydration. Added H atoms significantly augment decomposition, mainly by abstraction of the tertiary and primary hydrogens, reactions that, respectively, lead to acetone and propene as stable organic products. Traces of acetaldehyde were observed in some experiments above ≈ 1100 K and establish branching limits for minor decomposition pathways. To quantitatively account for secondary chemistry and optimize rate constants of interest, we employed the method of uncertainty minimization using polynomial chaos expansions (MUM‐PCE) to carry out a unified analysis of all datasets using a chemical model–based originally on JetSurF 2.0. We find: k(isopropanol → propene + H2O) = 10(13.87 ± 0.69) exp(?(33 099 ± 979) K/ T) s?1 at 979‐1212 K and 286‐484 kPa, with a factor of two uncertainty (2σ), including systematic errors. For H atom reactions, optimization yields: k(H + isopropanol → H2 + p‐C3H6OH) = 10(6.25 ± 0.42) T2.54 exp(?(3993 ± 1028) K /T) cm3 mol?1 s?1 and k(H + isopropanol → H2 + t‐C3H6OH) = 10(5.83 ± 0.37) T2.40 exp(?(1507 ± 957) K /T) cm3 mol?1 s?1 at 918‐1142 K and 183‐323 kPa. We compare our measured rate constants with estimates used in current combustion models and discuss how hydrocarbon functionalization with an OH group affects H abstraction rates.  相似文献   

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