Moderation of Hot Methyl Radicals in Photolysis of Methyl Iodide

1953 ◽  
Vol 21 (10) ◽  
pp. 1894-1894 ◽  
Author(s):  
Frank P. Hudson ◽  
Russell R. Williams ◽  
William H. Hamill
Keyword(s):  
Methyl Iodide ◽  
Methyl Radicals

High Temperature Absorption of the 3.39 µm He-Ne Laser Line by Small Hydrocarbons

1978 ◽  
Vol 32 (5) ◽  
pp. 489-493 ◽  
Author(s):  
D. B. Olson ◽  
W. G. Mallard ◽  
W. C. Gardiner
Keyword(s):  
High Temperature ◽  
Temperature Dependence ◽  
Methyl Iodide ◽  
Transient Absorption ◽  
Broad Band ◽  
Laser Line ◽  
Methyl Radicals ◽  
Large Numbers ◽  
Absorbing States ◽  
No Absorption

Absorptivity measurements for the 3.39 µm He-Ne laser line are reported for methane, acetylene, ethylene, ethane, propane, n-butane, and n-pentane over the temperature range 300 < T < 2000°K. Shock-heated mixtures containing formaldehyde and methyl iodide showed no absorption or transient absorption at any temperature that could be attributed to formaldehyde or methyl radicals. The temperature dependence of the absorptivities of the C2 and higher hydrocarbons was much weaker than for methane. Comparison with simple theoretical expectations and broad-band absorptivities showed that the higher hydrocarbon absorptions include quite large numbers of absorbing states.

Elementary reactions in the photochemical oxidation of methyl iodide

1958 ◽  
Vol 244 (1238) ◽  
pp. 411-423 ◽  
Keyword(s):  
Methyl Iodide ◽  
Relative Rate ◽  
Molecular Iodine ◽  
Photochemical Oxidation ◽  
Main Reaction ◽  
Methyl Radicals ◽  
Iodine Molecule ◽  
Methyl Radical ◽  
Elementary Reactions ◽  
Molecule Reaction

The photochemical oxidation of gaseous methyl iodide at room temperature was investigated under conditions such that oxygen molecules were competing with iodine molecules and/or iodine atoms for reaction with methyl radicals. The molecular iodine produced in the oxidation was measured by means of its light absorption. A balanced photomultiplier system for the determination of small percentage light absorptions is described. Analysis of the results shows that the contribution of the methyl radical + iodine atom recombination is negligible compared with the methyl radical + iodine molecule reaction for the relative concentrations of iodine atoms and iodine molecules involved. The variation with pressure of the ratio of the rate constant of the methyl radical + iodine molecule reaction to that of the methyl radical + oxygen molecule reaction indicates that the main reaction of methyl radicals with oxygen is a third-order one. This is assumed to be their association to form methylperoxy radicals. Methyl iodide is approximately ten times as efficient as carbon dioxide in acting as a third body for this association. The relative rate of a simultaneous second-order reaction of methyl radicals with oxygen has also been determined. From comparison with other work, the probable orders of magnitude of the rate constants of these elementary reactions of the methyl radical are deduced.

The photochemical decomposition of methyl iodide in presence of nitric oxide I. The reaction of methyl radicals with nitric oxide

1959 ◽  
Vol 249 (1257) ◽  
pp. 248-257 ◽  
Keyword(s):  
Nitric Oxide ◽  
Methyl Iodide ◽  
Molecular Iodine ◽  
Gas Mixture ◽  
Methyl Radicals ◽  
Third Order ◽  
Absolute Value ◽  
Uncertainty Factor ◽  
Photochemical Decomposition ◽  
Limiting Value

The quantum yield of molecular iodine produced in the photolysis of gaseous methyl iodide is markedly increased by the presence of small quantities of nitric oxide. The yield of iodine is determined by the competition between reactions of methyl radicals with iodine molecules to reform methyl iodide and of methyl radicals with nitric oxide to form nitrosomethane. The latter reaction is pressure-dependent and the kinetics may be interpreted in terms of the following steps: CH 3 + NO = CH 3 NO' ( k a ). CH 3 NO' = CH 3 + NO ( k b ), CH 3 NO' + M = CH 3 NO + M' ( k c,M ). The apparent third-order constant at low pressure { = ( k c, M k a ) / k b } is 50 times as great as that measured for the association of methyl radicals with oxygen in the same gas mixture. The minimum lifetime of the energy-rich CH 3 NO' complex is 10 -8 s. The absolute value of k a , the limiting value of the apparent second-order constant for the association, is estimated to be 7 x 10 11 ml. mole -1 s -1 , with an uncertainty factor of 3.

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.

Multiphoton ionization of methyl iodide and selective stepwise ionization of methyl radicals

1982 ◽  
Vol 76 (5) ◽  
pp. 2399-2406 ◽  
Author(s):  
J. Danon ◽  
H. Zacharias ◽  
H. Rottke ◽  
K. H. Welge
Keyword(s):  
Methyl Iodide ◽  
Multiphoton Ionization ◽  
Methyl Radicals ◽  
Stepwise Ionization

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 .

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