Temperature-Dependent, Site-Specific Rate Coefficients for the Reaction of OH (OD) with Methyl Formate Isotopologues via Experimental and Theoretical Studies.

Methyl esters are an important component of combustion and atmospheric systems. Reaction with the OH radical plays an important role in the removal of the simplest methyl ester, methyl formate (MF, CHOCHO). In this paper, the overall rate coefficients for the reactions of OH and OD with MF isotopologues, studied under pseudo-first-order conditions, are reported using two different laser flash photolysis systems with the decay of OH monitored by laser-induced fluorescence.

Kinetics of the Gas-Phase Reactions of - and -CHCHOO Criegee Intermediate Conformers with SO as a Function of Temperature and Pressure.

Kinetics of reactions between SO and CHCHOO Criegee intermediate conformers have been measured at temperatures between 242 and 353 K and pressures between 10 and 600 Torr using laser flash photolysis of CHCHI/O/N/SO gas mixtures coupled with time-resolved broadband UV absorption spectroscopy. The kinetics of -CHCHOO + SO are pressure-dependent and exhibit a negative temperature dependence, with the observed pressure dependence reconciling apparent discrepancies between previous measurements performed at ∼298 K. Results indicate a rate coefficient of (4.

Studies on the Kinetics of the CH + H Reaction and Implications for the Reverse Reaction, CH + H.

The reaction of CH radicals with H has been studied by the use of laser flash photolysis, probing CH decays under pseudo-first-order conditions using laser-induced fluorescence (LIF) over the temperature range 298-748 K at pressures of ∼5-100 Torr. Careful data analysis was required to separate the CH LIF signal at ∼428 nm from broad background fluorescence, and this interference increased with temperature. We believe that this interference may have been the source of anomalous pressure behavior reported previously in the literature (Brownsword, R.

Kinetics and Product Branching Ratio Study of the CHO Self-Reaction in the Highly Instrumented Reactor for Atmospheric Chemistry.

The fluorescence assay by gas expansion (FAGE) method for the measurement of the methyl peroxy radical (CHO) using the conversion of CHO into methoxy radicals (CHO) by excess NO, followed by the detection of CHO, has been used to study the kinetics of the self-reaction of CHO. Fourier transform infrared (FTIR) spectroscopy has been employed to determine the products methanol and formaldehyde of the self-reaction. The kinetics and product studies were performed in the Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC) in the temperature range 268-344 K at 1000 mbar of air.

Unimolecular Kinetics of Stabilized CHCHOO Criegee Intermediates: -CHCHOO Decomposition and -CHCHOO Isomerization.

The kinetics of the unimolecular decomposition of the stabilized Criegee intermediate -CHCHOO has been investigated at temperatures between 297 and 331 K and pressures between 12 and 300 Torr using laser flash photolysis of CHCHI/O/N gas mixtures coupled with time-resolved broadband UV absorption spectroscopy. Fits to experimental results using the Master Equation Solver for Multi-Energy well Reactions (MESMER) indicate that the barrier height to decomposition is 67.2 ± 1.

Kinetics of the gas phase reaction of the Criegee intermediate CHOO with SO as a function of temperature.

The kinetics of the gas phase reaction of the Criegee intermediate CHOO with SO have been studied as a function of temperature in the range 223-344 K at 85 Torr using flash photolysis of CHI/O/SO/N mixtures at 248 nm coupled to time-resolved broadband UV absorption spectroscopy. Measurements were performed under pseudo-first-order conditions with respect to SO, revealing a negative temperature dependence. Analysis of experimental results using the Master Equation Solver for Multi-Energy well Reactions (MESMER) indicates that the observed temperature dependence, combined with the reported lack of a pressure dependence in the range 1.

Kinetics of the Gas Phase Reactions of the Criegee Intermediate CHOO with O and IO.

The kinetics of the gas phase reactions of the Criegee intermediate CHOO with O and IO have been studied at 296 K and 300 Torr through simultaneous measurements of CHOO, the CHOO precursor (CHI), O, and IO using flash photolysis of CHI/O/O/N mixtures at 248 nm coupled to time-resolved broadband UV absorption spectroscopy. Experiments were performed under pseudo-first-order conditions with respect to O, with the rate coefficients for reactions of CHOO with O and IO obtained by fitting to the observed decays of CHOO using a model constrained to the measured concentrations of IO. Fits were performed globally, with the ratio between the initial concentration of O and the average concentration of IO varying in the range 30-700, and gave = (3.

CHOO Criegee intermediate UV absorption cross-sections and kinetics of CHOO + CHOO and CHOO + I as a function of pressure.

The UV absorption cross-sections of the Criegee intermediate CHOO, and kinetics of the CHOO self-reaction and the reaction of CHOO with I are reported as a function of pressure at 298 K. Measurements were made using pulsed laser flash photolysis of CHI/O/N gas mixtures coupled with time-resolved broadband UV absorption spectroscopy at pressures between 6 and 300 Torr. Results give a peak absorption cross-section of (1.

Temperature and Pressure Dependent Kinetics of QOOH Decomposition and Reaction with O: Experimental and Theoretical Investigations of QOOH Radicals Derived from Cl + (CH)COOH.

QOOH radicals are key species in autoignition, produced by internal isomerizations of RO radicals, and are central to chain branching reactions in low-temperature combustion. The kinetics of QOOH radical decomposition and reaction with O have been determined as a function of temperature and pressure, using observations of OH radical production and decay following H-atom abstraction from -butyl hydroperoxide ((CH)COOH) by Cl atoms to produce QOOH (CH(CH)COOH) radicals. The kinetics of QOOH decomposition have been investigated as a function of temperature (251-298 K) and pressure (10-350 Torr) in helium and nitrogen bath gases, and those of the reaction between QOOH and O have been investigated as a function of temperature (251-304 K) and pressure (10-100 Torr) in He and N.

An instrument to measure fast gas phase radical kinetics at high temperatures and pressures.

Fast radical reactions are central to the chemistry of planetary atmospheres and combustion systems. Laser-induced fluorescence is a highly sensitive and selective technique that can be used to monitor a number of radical species in kinetics experiments, but is typically limited to low pressure systems owing to quenching of fluorescent states at higher pressures. The design and characterisation of an instrument are reported using laser-induced fluorescence detection to monitor fast radical kinetics (up to 25 000 s(-1)) at high temperatures and pressures by sampling from a high pressure reaction region to a low pressure detection region.

Branching ratios in reactions of OH radicals with methylamine, dimethylamine, and ethylamine.

The branching ratios for the reaction of the OH radical with the primary and secondary alkylamines: methylamine (MA), dimethylamine (DMA), and ethylamine (EA), have been determined using the technique of pulsed laser photolysis-laser-induced fluorescence. Titration of the carbon-centered radical, formed following the initial OH abstraction, with oxygen to give HO2 and an imine, followed by conversion of HO2 to OH by reaction with NO, resulted in biexponential OH decay traces on a millisecond time scale. Analysis of the biexponential curves gave the HO2 yield, which equaled the branching ratio for abstraction at αC-H position, r(αC-H).

Measurement of hypoiodous acid concentration by a novel type iodide selective electrode and a new method to prepare HOI. Monitoring HOI levels in the Briggs-Rauscher oscillatory reaction.

A new type of iodide selective electrode prepared by dipping a silver wire into molten silver iodide is reported. The electrode was calibrated for silver and iodide ions and the measured electromotive force for various Ag(+) and I(-) concentrations was close to the theoretical within a few millivolts. Besides Ag(+) and I(-) ions, however, the electrode also responds to hypoiodous acid.

The nature of the sodium dodecylsulfate micellar pseudophase as studied by reaction kinetics.

The nature of the rate-retarding effects of anionic micelles of sodium dodecyl sulfate (SDS) on the water-catalyzed hydrolysis of a series of substituted 1-benzoyl-1,2,4-triazoles (1a-f) has been studied. We show that medium effects in the micellar Stern region of SDS can be reproduced by simple aqueous model solutions containing small-molecule mimics for the surfactant headgroups and tails, namely sodium methyl sulfate (NMS) and 1-propanol, in line with our previous kinetic studies for cationic surfactants ( Buurma et al. J.

Iodomalonic acid as an anti-inhibitor in the resorcinol inhibited Briggs-Rauscher reaction.

It was found that the inhibitory effect of resorcinol is less pronounced if it is added in a later stage of the Briggs-Rauscher reaction, which indicates that an accumulating intermediate--most probably iodomalonic acid--can suppress the inhibition. In fact, when iodomalonic acid was added to the reaction mixture, the inhibitory period was shortened considerably even at micromolar levels of the iodomalonic acid concentration. Moreover, iodomalonic acid can accelerate the rate of the reaction when applied in the same low concentrations, suggesting that it can be an autocatalytic intermediate of the Briggs-Rauscher reaction.

Reaction routes leading to CO2 and CO in the Briggs-Rauscher oscillator: analogies between the oscillatory BR and BZ reactions.

With Fenton-type experiments, it is shown that the intense CO2/CO evolution in the Briggs-Rauscher (BR) reaction is due to decarboxylation/decarbonylation of organic free radicals. The metal ion applied in the Fenton-type experiments was Fe2+ or Ti3+ or Mn2+ combined with H2O2 or S2O(8)(2-) as a peroxide, whereas the organic substrate was malonic acid (MA) or a 1:1 mixture of MA and iodomalonic acid (IMA). Experiments with a complete BR system applying MA or the MA/IMA mixture indicate that practically all CO2 and CO comes from IMA.

I(+1) transfer from diiodomalonic acid to malonic acid and a complete inhibition of the CO and CO2 evolution in the Briggs-Rauscher reaction by resorcinol.

A recent report on an intense CO 2 and CO evolution in the Briggs-Rauscher (BR) reaction revealed that iodination of malonic acid (MA) is not the only important organic reaction in the classical BR oscillator. To disclose the source of the gas evolution, iodomalonic (IMA) and diiodomalonic (I2MA) acids were prepared by iodinating MA with nascent iodine in a semibatch reactor. The nascent iodine was generated by an iodide inflow into the reactor, which contained a mixture of MA and acidic iodate.

The source of the carbon monoxide in the classical Belousov-Zhabotinsky reaction.

CO and CO2 evolution was measured in a cerium and in a ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction. These gases were stripped from the reaction mixture by a N2 carrier gas, mixed with H2, converted to methane on a Ni catalyst, and then measured by a flame ionization detector (FID). CO could be detected separately by absorbing CO2 on a soda lime column.

Periodic CO and CO2 evolution in the oscillatory Briggs-Rauscher reaction.

While various reactions in the inorganic subset of the oscillatory Briggs-Rauscher (BR) reaction were clarified in the recent years, the organic subset of the present mechanisms contains only one process: the iodination of malonic acid. Further organic reactions can play a role, however, if malonic (MA) and iodomalonic (IMA) acids can be oxidized in the BR reaction. As CO2 and CO should be products if such oxidations can take place, the main aim of this work was to learn whether these gases are produced in a significant amount in a BR system.

Contribution to the chemistry of the Belousov-Zhabotinsky reaction. Products of the Ferriin-Bromomalonic acid and the Ferriin-Malonic acid reactions.

In the present mechanistic schemes of the ferroin-catalyzed oscillatory Belousov-Zhabotinsky (BZ) reaction the oxidation of the organic substrates (bromomalonic or malonic acid) by ferriin (the oxidized form of the catalyst) plays an important role. As the organic products of these reactions were not yet identified experimentally, they were studied here by an HPLC technique. It was found that the main organic oxidation product of bromomalonic acid is bromo-ethene-tricarboxylic acid (BrEETRA), the same compound that is formed when bromomalonic acid is oxidized by Ce4+ (another catalyst of the BZ reaction).

Uncatalyzed reactions in the classical Belousov-Zhabotinsky system. I. Reactions of bromomalonic acid with acidic bromate and with HOBr.

The uncatalyzed reactions of bromomalonic acid (BrMA) with acidic bromate and with hypobromous acid were studied in 1 M sulfuric acid, a usual medium for the oscillatory Belousov-Zhabotinsky (BZ) reaction, by following the rate of the carbon dioxide evolution associated with these reactions. In addition, the decarboxylation rate of dibromomalonic acid (Br2MA) was also measured to determine the first-order rate constant of its decomposition (4.65 x 10(-5) s(-1) in 1 M H2SO4).

Uncatalyzed reactions in the classical Belousov-Zhabotinsky system. 2. The malonic acid-bromate reaction in acidic media.

The title reaction was studied with various techniques in 1 M sulfuric acid, a usual medium for the oscillatory Belousov-Zhabotinsky (BZ) reaction. It was found to be a more complex process than the bromomalonic acid (BrMA)-BrO3- reaction studied previously in the first part of this work. Malonic acid (MA) can react with acidic bromate by two parallel mechanisms.