The combustion of gaseous methyl iodide studied by flash photolysis and kinetic spectroscopy

1961 ◽  
Vol 263 (1312) ◽  
pp. 51-57 ◽  
Keyword(s):  
Free Radicals ◽  
Gas Phase ◽  
Methyl Iodide ◽  
Flash Photolysis ◽  
Oh Radicals ◽  
Methyl Radicals ◽  
Kinetic Spectroscopy ◽  
Slow Combustion ◽  
Low Pressures ◽  
Explosive Combustion

The combustion of gaseous methyl iodide has been studied under conditions of slow and explosive combustion and the behaviour of the methyl iodide, the free radicals OH and IO and the products formaldehyde and iodine has been followed by kinetic spectroscopy. At fairly low pressures ( l.0 to 5.5 cm Hg) the behaviour of the methyl iodide and the OH radicals under conditions of slow and explosive combustion indicates that the reaction between methyl radicals and oxygen proceeds by CH 3 + O 2 → H 2 CO + OH. At higher pressures, under slow combustion conditions, formaldehyde is detectable in the gas phase by reaction between methyl radicals and oxygen. Under slow combustion condi­tions also, the behaviour of the IO radicals and iodine suggests that the iodine atoms produced by the primary photolytic dissociation of m ethyl iodide are temporarily removed in the form of IO radicals, from which the final product iodine is then formed by 2IO → I 2 + O 2 .

The combustion of gaseous aldehydes studied by flash photolysis and kinetic spectroscopy

1960 ◽  
Vol 254 (1277) ◽  
pp. 147-162 ◽  
Keyword(s):  
Free Radicals ◽  
Formic Acid ◽  
High Temperatures ◽  
Flash Photolysis ◽  
Kinetic Mechanism ◽  
Kinetic Spectroscopy ◽  
Elementary Reactions ◽  
Slow Reaction ◽  
Explosive Reaction ◽  
Explosive Combustion

The identity and behaviour of free radicals produced during the combustion of gaseous aldehydes has been examined. The flash-initiated combustion of formaldehyde was investigated under conditions of slow and explosive combustion. The behaviour of formaldehyde and the derived radicals OH and HCO was followed during the course of the reaction. It was found that HCO radicals react rapidly with oxygen during the slow reaction, but decompose into H atoms and CO at the high temperatures produced during the explosive reaction. Further information on the reaction between HCO radicals and oxygen was obtained by flash - photolyzing gaseous formic acid in presence of oxygen and nitrogen under isothermal conditions. The results of this investigation are consistent with the kinetic observations previously made by Axford & Norrish. With one modification relating to the participation of HCO radicals they confirm the kinetic mechanism previously deduced by these authors. The flash-initiated combustion of acetaldehyde was also investigated under conditions of slow and explosive combustion, and information on several of the elementary reactions proceeding under these conditions has been obtained.

FREE RADICALS BY MASS SPECTROMETRY: XXII. PRIMARY DECOMPOSITION STEPS IN THE MERCURY-PHOTOSENSITIZED DECOMPOSITION OF METHANOL AND DIMETHYL ETHER

1961 ◽  
Vol 39 (1) ◽  
pp. 102-109 ◽  
Author(s):  
R. F. Pottie ◽  
A. G. Harrison, ◽  
F. P. Lossing
Keyword(s):  
Mass Spectrometry ◽  
Free Radicals ◽  
Dimethyl Ether ◽  
Excited Molecule ◽  
Primary Decomposition ◽  
Oh Radicals ◽  
No Formation ◽  
Abstraction Reaction ◽  
Reaction Proceeds ◽  
Low Pressures

The Hg 3P1 photosensitized decomposition of methanol at low pressures proceeds mainly by a dissociation into CH3O radicals and H atoms. No formation of CH2OH radicals is observed. A subsidiary reaction to form CH3 and OH may also be a primary step. Formation of CH2OH radicals at higher pressures is attributed to an abstraction reaction of CH3O with CH3OH.Two primary modes of dissociation are found to occur for dimethyl ether:[Formula: see text]The relative probabilities of occurrence at low pressures are ∼45% and ∼50%, respectively. The possibility that the second reaction proceeds by formation of an excited molecule is discussed.

The photolysis and pyrolysis of nitromethane and methyl nitrite

1967 ◽  
Vol 299 (1458) ◽  
pp. 317-336 ◽  
Keyword(s):  
Nitric Oxide ◽  
Nitrogen Dioxide ◽  
Elevated Temperatures ◽  
Flash Photolysis ◽  
Stable Form ◽  
Methyl Radicals ◽  
Elimination Reaction ◽  
Kinetic Spectroscopy ◽  
Methyl Nitrite ◽  
A Minor

The photolysis and pyrolysis of nitromethane and methyl nitrite have been studied using the techniques of flash photolysis and kinetic spectroscopy. The results show that photolysis of nitromethane yields methyl radicals and nitrogen dioxide, and that these fragments undergo recombination and disproportionation reactions to form methyl nitrite, methoxyl, and nitric oxide. In the presence of added nitric oxide, the methyl radicals react principally with nitric oxide to form nitrosomethane, which subsequently dimerizes and also reacts further with nitric oxide to yield nitrogen dioxide. The evidence also suggests that nitrosomethane is removed by a relatively efficient reaction with nitrogen dioxide at elevated temperatures to produce nitromethane and nitric oxide. In the case of methyl nitrite, light absorption results not only in photolysis, but also in the formation of an isomer of the nitrite which then reverts slowly to the stable form. The nature of this isomer is not known, but possibilities are suggested and discussed. It is concluded that the decomposition (photolytic or pyrolytic) of methyl nitrite occurs by the rupture of the O—N bond, and that the methoxyl radicals formed disproportionate to yield methanol and form aldehyde. Nitroxyl is also formed but only as a minor product, and the marked increase in intensity of its spectrum in the presence of added nitric oxide shows that it is not formed by a molecular elimination reaction, but probably by CH 3 O + NO → CH 2 O + HNO.

A kinetic study of the reactions of OH radicals with fluoroethanes. Estimates of C—H bond strengths in fluoroalkanes

1983 ◽  
Vol 61 (5) ◽  
pp. 861-865 ◽  
Author(s):  
Jean-Pierre Martin ◽  
George Paraskevopoulos
Keyword(s):  
Kinetic Study ◽  
Gas Phase ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Oh Radicals ◽  
Bond Dissociation Energies ◽  
Time Resolved ◽  
Dissociation Energies ◽  
Bond Strengths ◽  
Vacuum Uv

A kinetic study of the reactions of OH radicals with a series of fluoroethanes in the gas phase is presented. OH radicals were generated by flash photolysis of H2O vapor in the vacuum uv (λ > 165 nm) and were monitored in absorption by time-resolved attenuation of resonance radiation at 308.15 nm [OH(A2Σ+ → X2Π)]. The following absolute rate constants (in units of 109 cm3mol−1 s−1 at the 95% confidence limit) were determined at [Formula: see text][Formula: see text][Formula: see text][Formula: see text][Formula: see text]From a linear correlation of the present and previously published rate constants with bond dissociation energies, the following quantities (in kcal mol−1 at 298 K) were estimated to be: D(CH3CHF—H) = 96.3 ± 1.5, D(CH2FCHF—H = 98.8 ± 1.0, D(CF3CHF—H) = 103.5 ± 1.0, D(CHF2CF2—H) = 103.0 ± 1.5, and [Formula: see text][Formula: see text]

ChemInform Abstract: FLASH PHOTOLYSIS OF ACETONE IN GAS PHASE, KINETICS OF ETHANE FORMATION FROM METHYL RADICALS

1975 ◽  
Vol 6 (13) ◽  
Author(s):  
MARJA-LIISA POHJONEN ◽  
LEILA LEINONEN ◽  
HELGE LEMMETYINEN ◽  
JOUKO KOSKIKALLIO
Keyword(s):  
Gas Phase ◽  
Flash Photolysis ◽  
Methyl Radicals ◽  
Gas Phase Kinetics ◽  
Ethane Formation ◽  
Kinetics Of

Reactions in Omcvd: Detection of Gas Phase Radicals In Gaas Deposition Under Single Gas-Surface Collision Conditions

1987 ◽  
Vol 101 ◽  
Author(s):  
D.W. Squire ◽  
C.S. Dulcey ◽  
M.C. Lin
Keyword(s):  
Gas Phase ◽  
Ionization Mass ◽  
Laser Ionization ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Arrhenius Activation Energy ◽  
Gallium Atom ◽  
Surface Collision ◽  
Low Pressures ◽  
Radical Yield

ABSTRACTLaser ionization mass spectrometry has been used to study the deposition of gallium from trimethylgallium with and without AsH3. The apparent Arrhenius activation energy for the production of gas-phase methyl radicals from trimethylgallium is measured to be 28 ± 2 kcal/mol in the presence of AsH3, about the same value as measured in the absence of AsH3. At a substrate temperature of 1150 K where gallium desorption is substantial, addition of AsH3 is found to increase methyl radical yield but drastically decrease gallium atom desorption. A mechanism is presented to describe the deposition of GaAs at low pressures under single gas-surface collision conditions.

The photochemical decomposition of methyl iodide in presence of nitric oxide - II. Reactions of nitrosomethane

1959 ◽  
Vol 249 (1257) ◽  
pp. 258-269 ◽  
Keyword(s):  
Nitric Oxide ◽  
Gas Phase ◽  
Methyl Iodide ◽  
Initial Rate ◽  
Wavelength Region ◽  
Order Reaction ◽  
Methyl Radicals ◽  
Second Order Reaction ◽  
Photochemical Decomposition ◽  
Rate Method

A product of the photolysis, in presence of a small quantity of nitric oxide, of methyl iodide reacts with excess nitric oxide to form a substance(s), Y , which absorbs light throughout the wavelength region 2300 to 5300 Å. The initial products of the photolysis, in presence of small quantities of nitric oxide, of both acetone and acetaldehyde react similarly. The species undergoing the reaction is believed to be monomeric nitrosomethane, formed by the association of methyl radicals with nitric oxide. The order of the reaction to form Y , as determined by the initial rate method, is one with respect to nitrosomethane and two with respect to nitric oxide. The extent of the reaction, which can be used as a measure of nitrosomethane concentration, depends on the concentration of nitric oxide. In absence of excess nitric oxide the monomer disappears slowly from the gas phase in a second-order reaction, which is thought to be the dimerization to nitrosomethane dimer.

Rates of OH radical reactions. VII. Reactions of OH and OD radicals with n-C4H10, n-C4D10, H2 and D2, and of OH with neo-C5H12 at 297 K

1980 ◽  
Vol 58 (20) ◽  
pp. 2146-2149 ◽  
Author(s):  
George Paraskevopoulos ◽  
Wing S. Nip
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Room Temperature ◽  
Kinetic Isotope Effect ◽  
Flash Photolysis ◽  
Deuterium Atom ◽  
Oh Radicals ◽  
Confidence Limits ◽  
Kinetic Isotope ◽  
Absorption Technique

Absolute rate constants of hydrogen and deuterium atom abstraction by OH and OD radicals from n-C4H10, n-C4D10, H2 and D2, and by OH radicals from neo-C5H12 have been measured at room temperature in the gas phase using the flash photolysis-resonance absorption technique. The rate constants in units of cm3 mol−1 s−1 were found to be:[Formula: see text]The quoted errors are the 95% confidence limits. A kinetic isotope effect was observed when hydrogen was replaced by deuterium in the paraffin and H2, whereas there was no significant effect when OH was replaced by OD.

scholarly journals Predicting arene rate coefficients with respect to hydroxyl and other free radicals in the gas-phase: a simple and effective method using a single topological descriptor

2007 ◽  
Vol 7 (13) ◽  
pp. 3559-3569 ◽  
Author(s):  
M. R. McGillen ◽  
C. J. Percival ◽  
G. Pieterse ◽  
L. A. Watson ◽  
D. E. Shallcross
Keyword(s):  
Free Radicals ◽  
Gas Phase ◽  
Aromatic Hydrocarbons ◽  
Atmospheric Model ◽  
Quantitative Structure Activity Relationship ◽  
Rate Coefficients ◽  
Oh Radicals ◽  
Novel Approach ◽  
The Impact ◽  
Strong Relationships

Abstract. The reactivity of aromatic compounds is of great relevance to pure and applied chemical disciplines, yet existing methods for estimating gas-phase rate coefficients for their reactions with free radicals lack accuracy and universality. Here a novel approach is taken, whereby strong relationships between rate coefficients of aromatic hydrocarbons and a Randić-type topological index are investigated, optimized and developed into a method which requires no specialist software or computing power. Measured gas-phase rate coefficients for the reaction of aromatic hydrocarbons with OH radicals were correlated with a calculated Randić-type index, and optimized by including a term for side chain length. Although this method is exclusively for use with hydrocarbons, it is more diverse than any single existing methodology since it incorporates alkenylbenzenes into correlations, and can be extended towards other radical species such as O(3P) (and tentatively NO3, H and Cl). A comparison (with species common to both techniques) is made between the topological approach advocated here and a popular approach based on electrophilic subsituent constants, where it compares favourably. A modelling study was carried out to assess the impact of using estimated rate coefficients as opposed to measured data in an atmospheric model. The difference in model output was negligible for a range of NOx concentrations, which implies that this method has utility in complex chemical models. Strong relationships (e.g. for OH, R2=0.96) between seemingly diverse compounds including benzene, multisubstituted benzenes with saturated, unsaturated, aliphatic and cyclic substitutions and the nonbenzenoid aromatic, azulene suggests that the Randić-type index presented here represents a new and effective way of describing aromatic reactivity, based on a quantitative structure-activity relationship (QSAR).

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