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Kinetics of the thermal decomposition reaction CH2F2 → CHF + HF was studied by laser absorption measurements in a shock tube. The rate constants were determined by analyzing temporal profiles of HF produced in pyrolysis of CH2F2 over the temperature range 1577–2214 K at pressure of ∼100 kPa in Ar bath. The results were well reproduced by master equation analysis based on RRKM theory and classical trajectory calculations, which gave the following rate constant expressions: k∞ = 2.34 × 1015 exp(−41,550 K/T) s−1, k0 = 5.33 × 1025 (T/K)−8.635 exp(−44,190 K/T) cm3 molecule−1 s−1, and Fcent = 0.13.

The thermal decomposition of gaseous nitromethane and the subsequent bimolecular reaction between CH3 and NO2 have been experimentally studied using time-resolved cavity-enhanced absorption spectroscopy behind reflected shock waves in the temperature range 1336–1827 K and at a pressure of 100 kPa. Temporal evolution of NO2 was observed following the pyrolysis of nitromethane (diluted to 80–140 ppm in argon) by monitoring the absorption around 400 nm. The primary objectives of the current work were to evaluate the rate constant for the CH3 + NO2 reaction (k2) and to examine the contribution of the roaming isomerization pathway in nitromethane decomposition. The resultant rate constant can be expressed as k2 = (9.3 ± 1.8) × 10–10(T/K)−0.5 cm3 molecule–1 s–1, which is in reasonable agreement with available literature data. The decomposition of nitromethane was found to predominantly proceed with the C–N bond fission process with the branching fraction of 0.97 ± 0.06. Therefore, the upper limit of the branchi...

Hydrogen abstraction reactions from hydrofluorocarbons are important reaction steps in both atmospheric and combustion chemistry. In this study, kinetics of the H-abstraction reactions from methane...

Motivated by recent shock tube studies on the thermal unimolecular decomposition of fluoroethanes, in which unusual trends have been reported for collisional energy-transfer parameters, the rate constants for the thermal decomposition of fluoroethane were investigated using a shock tube/laser absorption spectroscopy technique. The rate constants were measured behind reflected shock waves by monitoring the formation of HF by IR absorption at the R(1) transition in the fundamental vibrational band near 2476 nm using a distributed-feedback diode laser. The peak absorption cross sections of this absorption line have also been determined and parametrized using the Rautian-Sobel'man line shape function. The rate constant measurements covered a wide temperature range of 1018-1710 K at pressures from 100 to 290 kPa, and the derived rate constants were successfully reproduced by the master equation calculation with an average downward energy transfer, ⟨ΔEdown⟩, of 400 cm(-1).

The combustion characteristics and reaction mechanism of mixtures containing nitrogen trifluoride (NF 3 ) were investigated. Burning velocities for H 2 /NF 3 /N 2 , CH 4 /NF 3 /N 2 , and C 3 H 8 /NF 3 /N 2 flames were determined for the first time at various equivalence ratios and N 2 mole fractions. The burning velocities of the latter two flames were similar and showed peaks at equivalence ratios of ∼1.0, while those of the H 2 /NF 3 /N 2 flames had the pronounced peak at low equivalence ratios where the formation of the wrinkled flames was observed. A detailed kinetic model was constructed to simulate the laminar burning velocities of H 2 /NF 3 /N 2 and CH 4 /NF 3 /N 2 flames. The model accurately reproduced the experimental results. Analyses of the reaction mechanism revealed the major reaction pathways that involve the decomposition of NF 3 , the oxidation and chain-fluoridation of H 2 and CH 4 , and the formation of N 2 .

Dimethyl ether (DME) has been focused as a substitute for diesel fuel, and a number of studies have investigated engines fueled with DME because DME has a low auto-ignition temperature and does not generate particulate matter (PM). Therefore, in the last few years, the construction of DME filling stations for trucks in Japan has been planned. The introduction of DME vehicles requires expansion of DME supply stations, which in turn requires the collection of safety data and the establishment of safety regulations. The present paper describes an experimental investigation of the hypothetical scenario in which liquid DME is accidentally released and an explosion occurs. In the present study, large-scale leakage and ignition of DME were investigated and flame propagation data was obtained. We also measured the overpressure of the blast wave and the heat flux from the fireball. When the ignition position is near the nozzle, the flame propagation velocity is higher. The overpressure from the DME fireball is stronger than that from DME/air mixture deflagration. In summary, these results provide safety data for safety management of DME filling stations.

Dimethyl ether (DME) has been considered as a substitute for diesel fuel because it has a low auto-ignition temperature and produces less NO x , SO x , and particulate matter. However, the introduction of DME vehicles needs widely available DME supply stations. Moreover, the preparation of safety regulations for DME supply stations is very important, and so safety data is needed. Therefore, the present paper reports the hazards of the DME jet diffusion flame, which is one of several hazardous properties of DME, by studying the results of leaking gas and liquid DME. DME jets were released horizontally from circular nozzles whose diameters were 0.2, 0.4, 0.8 and 2 mm, and the release pressure was varied from the saturated vapor pressure to 2 MPa. When gaseous DME was released at the saturated vapor pressure, the flame was blown out. However, when liquefied DME was released, the flame formed. We obtained the experimental equations for estimating the scale and thermal hazards of DME diffusion flames.

While extensive studies have been conducted concerning the formation of detonation waves in various combustible gaseous mixtures under static conditions since the 1950s, there is very little experimental work on simple flowing systems. In this study, experiments on the deflagration to detonation transition (DDT) of a hydrogen–air flow system were carried out to see the effects of tube diameter, equivalence ratio, and flow types in a premixed and non-premixed flow. Tube diameters used were 25, 50, and 100 mm. The premixed experiments show that the larger tube diameter provides a wider range in run-up distance, reduction of L DDT/D (ratio of the run-up distance, L DDT to tube diameter), and expansion of the detonable concentration limit by spreading the cell width. The result of the non-premixed experiments show that similar values of the run-up distance to the premixed experiments are obtained at an equivalence ratio of about 1.0, however, fluctuations of DDT occur near the DDT concentration limit. Under laminar flow conditions at a Reynolds number of less than 2,300, the difference between the two systems could not be observed. However, when the Reynolds number increases towards turbulent conditions, the DDT run-up distance decreases compared to that of static flow conditions.

The phenomenon of self-ignition and explosion during discharge of high-pressure hydrogen was investigated. To clarify the ignition conditions of high-pressure hydrogen jets, rapid discharge of the high-pressure hydrogen was examined experimentally. A diaphragm was used to allow rapid discharge of the high-pressure hydrogen. The burst pressure was varied from 4 to 30 MPa. The downstream geometry of the diaphragm was a flange and extension pipes, with the pipe length varying from 3 to 300 mm. The diameter of the nozzle was 5 or 10 mm. When short pipes were used, the hydrogen jet did not ignite. However, the hydrogen jet showed an increasing tendency to ignite in the pipe as the length of the pipe became longer. At higher burst pressures, a diffusion jet flame was formed from the pipe. The blast wave from the fireball formed on self-ignition of the hydrogen jet resulted in an extremely rapid pressure rise.

1,1,1-Trifluoroethane (CH3CF3) has been frequently used as a chemical thermometer or an internal standard in shock tube studies to determine relative rates of chemical reactions. The rate constants for the thermal decomposition of CH3CF3 were recently reported to have anomalous pressure dependence in the high-temperature falloff region. In the present study, the kinetics of the CH3CF3 decomposition were reinvestigated using shock tube/laser absorption (ST/LA) spectroscopy and single-pulse shock tube (SPST) methods over the temperature range 1163-1831 K at pressures from 95 to 290 kPa. The present rate constants are 2-3 times smaller than those reported in previous single-pulse experiments performed at near high-pressure limit conditions. The recommended rate constant expression, k = 5.71 × 10(46)T(-9.341) exp(-47073 K/T) s(-1), was obtained over the temperature range 1000-1600 K with uncertainties of ±40% at temperatures below 1300 K and ±32% at 1600 K. The rate constants at the high-temperature region showed clear falloff behavior and were in good agreement with recent high-temperature experiments. The falloff rate constants could not be reproduced by a standard RRKM/master-equation model; this study provides additional evidence for the unusual pressure dependence previously reported for this reaction. Additionally, the rate constants for the decomposition of 1,1-difluoroethylene (CH2CF2) were determined over the temperature range 1650-2059 K at pressures of 100 and 205 kPa, and were reproduced by the RRKM/master-equation calculation with an average downward energy transfer of 900 cm(-1).

The overall rate constants for reactions of O ( 3 P ) with three fluoroethanes, O ( 3 P )+ CH 3 CH 2 F → OH + CH 2 CH 2 F / CH 3 CHF (1), O ( 3 P )+ CH 2 FCH 2 F → OH + CHFCH 2 F (2), and O ( 3 P )+ CH 3 CHF 2 → OH + CH 2 CHF 2 / CH 3 CF 2 (3), were measured by laser flash photolysis in shock heated sample gases at 1000–1400 K. The rate constants were obtained in the simple Arrhenius form, k=Aexp(−Ea/RT), where A=2.19×10−9, 1.24×10−9 and 7.43×10 −9 cm 3 molecule −1 s −1 and Ea=58.0, 57.0 and 82.7 kJ mol−1, and uncertainty factors for k at 2σ level are F=1.36, 1.27 and 1.19, respectively. The effect of substitution of the fluorine atom on the overall rate constant is discussed in comparison with the corresponding rates for a series of alkanes and fluoromethanes.

Vibrationally excited species have been considered to play significant roles in H2/F2 reaction systems. In the present study, in order to obtain further understanding of the chain reaction mechanism in the combustion of mixtures containing H2 and F2, burning velocities for H2/F2/O2/N2 flames were measured and compared to that obtained from kinetic simulations using a detailed kinetic model, which involves the vibrationally excited species, HF(ν) and H2(ν), and the chain-branching reactions, HF(ν > 2) + F2 = HF + F + F (R1) and H2(ν = 1) + F2 = HF + H + F (R2). The results indicated that reaction R1 is not responsible for chain branching, whereas reaction R2 plays a dominant role in the chain reaction mechanism. The kinetic model reproduced the experimental burning velocities with the presumed rate constant of k2 = 6.6 × 10(-10) exp(-59 kJ mol(-1)/RT) cm(3) s(-1) for R2. The suggested chain-branching reaction was also investigated by quantum chemical calculations at the MRCI-F12+CV+Q/cc-pCVQZ-F12 level of theory.

To reexamine the possibility of the spin-forbidden, molecular-elimination mechanism of the thermal decomposition of H2S, H2S + M → S(3P) + H2 + M (1), recently indicated by experimental and theoretical studies, as well as to examine the cause of discrepancies of its rate constants among recent works, the reverse insertion channel of the S(3P) + H2 reaction, S(3P) + H2 + M → H2S + M (−1), has been investigated. The experiments have been conducted with an excimer-laser photolysis (248 nm) in a shock tube at a lower temperature range, 900−1050 K, and a higher pressure range up to 4 atm, than previous studies, where the insertion process (−1) was estimated to be dominant over the simple hydrogen-atom-transfer reaction, S(3P) + H2 → H + HS (2). The decay rate of S(3P) atoms has been measured by using an atomic resonance absorption spectrometry technique. The measured rate constant agreed well with the extrapolation of the previous measurements for reaction 2, showing that the recombination channel (−1) is stil...

The kinetics and the mechanism of the reaction of S( 3 P) with O 2 have been studied at low (293 K) and high (980–1610 K) temperatures. The strong non-Arrhenius behavior of the overall rate constant, which has been inferred from previous measurements, was confirmed. Possible causes of this non-Arrhenius behavior were investigated. No difference was found in the product channel between high and low temperatures, i.e., the products of the reaction were confirmed to be O( 3 P)+SO at both low (293 K) and high (1566 K) temperatures by quantitative measurements of O( 3 P) atoms. No pressure dependence was found either in the rate constant or in the product yield in the pressure range 2–50 Torr (Ar buffer) at 293 K. At low temperature, the time profile of each triplet component of S( 3 P J ) was measured separately. The intratriplet relaxations by collision with O 2 were found to be about one order of magnitude faster than the reaction with O 2 . An analysis of the intratriplet relaxation by O 2 strongly suggests the contribution of bound multiplet surfaces, which probably have substantial barriers toward products, O( 3 P)+SO. These (and/or other) multiplet surfaces probably contribute the steep rise of rate constant at higher temperatures.

The kinetics and the mechanism of the thermal decomposition of H2S and subsequent reactions have been studied. The rate constant for the initiation reaction H2S + M → products (1) was determined by a shock tube−infrared emission spectroscopy at temperatures 2740−3570 K to be k1 = 10-10.44±0.31 exp[−(268.6±18.4)kJ mol-1/RT] cm3 molecule-1 s-1, which is about one-fifth to one-tenth of the recent results reported by Woiki and Roth (J. Phys. Chem. 1994, 98, 12958) and Olschewski et al. (J. Phys. Chem. 1994, 98, 12964). An ab initio (MRCI+Q) calculation suggested that a spin-forbidden product channel (→S(3P) + H2) is energetically favorable compared to a H−S bond fission channel; that is, the singlet−triplet intersystem crossing occurs at an energy lower than the dissociation threshold for HS + H by about 17 kJ mol-1. The present rate constant for reaction 1 could be well reproduced by an unimolecular decomposition theory with the calculated energy for the crossing and with a reasonable collision parameter, βc...

Thermal decomposition of COS was investigated by shock tubes between 1140—3230 K. The decay of COS and S was monitored by IR emissions and atomic resonance absorption spectrometry (ARAS) coupled with laser flash photolysis technique, respectively. The rate constants for the reactions COS + M → CO + S + M (1) and COS + S → CO + S2 (2) were determined as k1 = (4.07 ± 1.83) × 10−10exp (−257 ± 24kJ/RT), T: 1900—3230 K and k2 = (3.91 ± 1.18) × 10−11exp (−28.3 ± 0.9 kJ/RT) cm3 molecule−1 s−1, T: 1140—1680 K.

We performed ab initio molecular orbital calculations to derive rate expressions for the reactions of N2O with O(3P) and CO. Major products of the O(3P) + N2O reactions are predicted to be NO + NO. Comparisons of calculated and experimental rate constants indicate good agreement exists with the most recent experimental values.