Irene R. Slagle

Kinetics of the reaction of methyl radicals with nitrogen dioxide

Abstract The mechanism of the reaction CH 3 + NO 2 →CH 3 O + NO was studied and its rate constant at 295 K was determined to be (2.5 ± 0.5) × 10 −11 cm 3 molecule −1 s −1 Methyl radicals were produced in a tubular reactor by IR multiphoton dissociation of C 6 F 5 OCH 3 , and concentration profiles were measured using photoionization mass spectrometry.

Kinetics of the reactions of SiH3 with O2 and N2O

Abstract The kinetics of the reactions SiH 3 + O 2 and SiH 3 + N 2 O have been investigated using time-resolved photoionization mass spectrometric detection of SiH 3 . Rate constants for the SiH 3 +O 2 reaction were determined from 296 to 500 K ( k = 4.96 × 10 −12 exp (275/ T ) cm 3 molecule −1 s −1 . An upper limit for the SiH 3 + N 2 O rate constant at 500 K was also established (5 × 10 −15 cm 3 molecule −1 s −1 ).

Kinetics of the reaction between oxygen atoms and carbon disulfide

The open channels of the room temperature 0+CS2 reaction have been identified by studying this reaction in high‐intensity undiscriminated crossed molecular beams using photoionization mass spectrometry to detect the products. Three open channels have been identified: O + CS2 → CS + SO (1); O + CS2 → OCS + S (2); and O + CS2 → CO + S2 (3). The overall rate constant (k) of the O + CS2 reaction as well as the branching ratio (k2/k) for Channel (2) were measured at 302°K using a fast‐flow reactor. They are k=4.0×10−12 cm3 p−1 sec−1, and k2/k=0.093. Speculation on the branching ratios for Channels (1) and (3) are offered based on the results of the crossed beam experiments. The possible roles of OCS production by Channel (2) and CO production by Channel (3) in the performance of the O+CS2 chemical laser are mentioned.

Kinetics of the reaction of C3H3 with molecular oxygen from 293–900 K

The kinetics and mechanism of the reaction of C3H3 with O2 were investigated from 293–900 K using a tubular reactor coupled to a photoionization mass spectrometer. From 293–333 K, the reaction proceeds by a simple reversible addition reaction. Between 380 and 430 K the equilibrium C3H3+O2 ahC3H3O2 was clearly observable, and equilibrium constants were measured as a function of temperature. These measurements yielded the values of ΔH298o (−79±6 kJ mole−1) and ΔS298o (−131±12 J mole−1 K−1) for this reaction. A mechanism change was observed as temperature rises. Above 350 K, H2C2O is observed as a new product whose importance increases rapidly with increasing temperature. Rate constants were measured as a function of density and temperature for the low temperature addition reaction and the high temperature reaction (from 500–900 K). An Arrhenius expression is recommended for the high temperature process (represented as C3H3+O2→H2C2O+HCO), 5×10−14exp(−12 kJmole−1/RT) cm3molecule−1 s−1, which is based on the results of this study and the kinetic model offered to explain the findings. A mechanism of the C3H3+O2 reaction is proposed which involves initial formation of a C3H3O2 adduct. At temperatures above 350 K, a cyclic rearrangement of the adduct, which leads to the formation of H2C2O+HCO, competes with its redissociation to C3H3+O2.

Experimental investigation of the kinetics and mechanism of the reaction of n-propyl radicals with molecular oxygen from 297 to 635 K

The kinetics and mechanism of the n-C3H7+O2 reaction were studied from 297 to 635 K to gain new knowledge of the change in mechanisms of R+O2 reactions as a function of temperature. Studies were conducted using a heated tubular reactoor coupled to a photoionization mass spectrometer. n-C3H7 and C3H6 concentrations were monitored in real-time experiments initiated by laser photolysis of the free-radical precursor. Overall rate constants were measured as a function of gas density (He or N2) from 1.2–12×1016 molec cm−3 at four temperatures: 297, 400, 550 and 635 K. The dependencies of the rate constants on pressure and temperature, up to 550K were those expected of the addition reaction n-C3H7+O2→C3H7O2 near the high pressure limit. The fraction of the n-C3H7+O2 reaction that proceeds by an alternate reactive route which produces C3H6+HO2 was determined at 297 K ( 0.00 ± 0.00 0.05 ) and at 550 K (0.14±0.05). At 635 K the R ⇌ RO2 equilibrium was observed together with a delayed production of C3H6. The ultimate fractional yield of C3H6 could not be observed at this temperature. It is estimated to be over 0.8. The results are discussed in terms of both an uncoupled parallel-path reaction mechanism leading to the two possible sets of reaction products and a coupled mechanism that proceeds via a common C3H7O2 adduct.

Shock‐Tube Study of the Acetylene‐Oxygen Reaction. IV. Kinetic Study of CH, C2, and Continuum Chemiluminescence During the Induction Period

The induction period of the C2H2+O2 reaction is accompanied by the exponential growth of chemiluminescent emission from several sources. The emission between 300 and 550 nm has been spectrally analyzed as well as dynamically monitored using an end‐on shock‐tube technique. Light emitted during the early portion of the induction period consists of emission from CH(A 2Δ), CH(B 2Σ−), and CH(C 2Σ+) superimposed on a weakly structured or unstructured emission (called the continuum) which has a maximum intensity near 350 nm. The exponential growth constants of these four emissions as well as their relative intensities were measured over a 1000°K temperature range (1100–2100°K), a tenfold range in [O2], and a twofold range in [C2H2]. All these emissions grow exponentially with the same growth constant as that of a major induction‐period product CO, indicating that they originate from reactions first order in reaction intermediates. The relative intensities of pairs of these four emissions were found to be indepen...

Direct determination of the rate constant for the reaction of oxygen atoms with carbon monosulphide

Abstract The overall rate constant for the reaction of oxygen atoms with carbon monosulphide has been directly determined in flow-reactor experiments at 305 K and found to be (2.06±0.14) × 10 −11 cm 3 molecule −1 s −1 .

Direct identification of products and measurement of branching ratios for the reaction of oxygen atoms with vinylbromide

Direct detection of the products of the O + C2H3Br reaction occurring in high-intensity room temperature crossed beams reveals that the reaction proceeds by three reactive channels, the products of which are, 1. CH3 + BrCO (and/or Br + CO); 2. CH2Br + HCO (and possibly H + CO), and 3. H2C2O + HBr. Flow reactor studies of the overall rate of the O + C2H3Br reaction and of the rate of CH3 and H2C2O production have yielded rate constants for the overall reaction, for route (1), and for route (3). These rate constants were used to calculate branching ratios for all three reactive channels.

Kinetics of the reactions of unsaturated free radicals (methylvinyl and i-C4H3) with molecular oxygen

The kinetics and mechanisms of the reactions of two unsaturated hydrocarbon free radicals, methylvinyl (CH3CH=CH) and i-C4H3 (CH2=C=C=CH) with molecular oxygen were investigated using a tubular reactor coupled to a photoionization mass spectrometer. Rate constants were measured as a function of temperature and density in time-resolved experiments. Searches were conducted for possible products to identify reactive routes. The methylvinyl+O2 reaction was studied betweeen 296 and 600 K. The rate constant is essentially constant throughout this range, 7.2(±1.4)×10−12 cm3 molecule−1 s−1. The only reactive route observed is that which yields CH3CHO and HCO, a route analogous to that of the C2H3+O2 reaction. The i-C4H3+O2 reaction rate constant was measured from 296 to 900 K and was found to decrease sharply with increasing temperature, from 4.5(±0.9)×10−12 cm3 molecule−1 s−1 at 296 to 6.4(±1.3)×10−13)×10−13 cm3 molecule−1 s−1 at 900 K corresponding to a T−1.8 power dependence in this temperature range. The reaction rate constants of both reactions studied did not depend on density. No products of the i-C4H3+O2 reaction could bedetected. Possible mechanisms of this reaction are discussed. The role of elementary reactions between unsaturated free radicals and molecular oxygen in combustion processes is briefly reviewed.

Direct identification of reactive routes in the reaction of oxygen atoms with dimethylamine

Abstract The gaseous reaction of oxygen atoms with dimethylamine was studied in a cross-jet reactor and found to proceed by electrophilic addition to form an energy-rich N-oxide which rearranges to an hydroxylamine and then decomposes via three routes: (CH 3 ) 2 N + OH, CH 3 NCH 2 + H 2 O and CH 3 NHO + CH 3 .