Mutual interactions of the methyl and methylperoxy radicals studied by flash photolysis and kinetic spectroscopy

Abstract

The decadic extinction coefficient of the methyl radical at 216.4 nm and the rate constant for mutual combination were redetermined as:The application of the Beer-Lambert law to these measurements was justified experimentally. The absorption spectrum of the methylperoxy radical was characterized as a weak, broad, structureless band, having a maximum at 240 nm with ~(240) = 1.55 X lo3 l./mol cm. The mutual interaction of methylperoxy radicals leads to the generation of methoxy and hydroperoxy radicals as a consequence of the nonterminating interaction 2 CH30O + 2 CH30. + 0 2 CH30 + 0 2 -j HCHO + HOO Each derivative radical may consume a significant fraction of the methylperoxy radicals, and either of these cross interactions may be made predominant by a suitable choice of oxygen pressure. The mutual interaction was studied under both conditions. The overall mechanism was analyzed by a precise computational method, and the rate constant of the total mutual interaction 2 CH3OO -all products was estimated as k q = (3.5 f 0.3) X lo8 l./mol sec

Is either direct photolysis or photocatalysed H-shift of peroxyl radicals a competitive pathway in the troposphere?

“…248 nm (with values around 1.2 × 10 −18 cm 2 ), part of the spectrum extends from 300 nm until about 349 nm. Our results agree reasonably with the experimental measurements of photolysis at least for C 2 H 5 O 2 , for which many studies have found a peak located around 240 nm, with values of 3-5 × 10 −18 cm 2 [15,[17][18][19][20][21][22][23][24][25][26][27][28]. Thus, our model works well for the photolysis cross-section estimation for polyatomic molecules.…”

The acetyl radicals CH3CO· and CD3CO· studied by flash photolysis and kinetic spectroscopy

“…4 ) = 9.8 X lo3 L/mol-cm and ~~~( 2 1 6 . 4 ) = 9.5 X lo3 L/mol.cm [5] Close agreement exists between the values of the rate constants for mutual interaction k? and k y .…”

“…The relationship between these maxima has prevented the characterization of the acetyl radical spectrum by the flash photolysis of acetaldehyde, which has been shown to generate both acetyl and formyl radicals [l]. In contrast, the maxima of the spectra of the hydroperoxy and methylperoxy radicals are described by the values ~HOO(210) = 1.2 X lo3 L/mol.cm [17] and ~~~~0 0 ( 2 4 0 ) = 1.5 X lo" L/mol.cm [5], and this relationship does not preclude the use of the absorbance of the methylperoxy radical to study its fast reactions in the presence of the hydroperoxy radical Corroborative spectra have been derived for the acetyl radical from the study of the flash photolysis of both methyl ethyl ketone and biacetyl. Values of A40(A) were measured for each system under conditions analogous to those used for the acetone system, and are shown in Figures 7 and 8.…”

“…without introducing significant error. The value k: = (3.2 f 0.4) X 1O1O L/mol-s was redetermined [5]from a study of the flash photolysis of azomethane by a method described previously [7]. An analogous pair of equations was used to calculate ky and k y from the results of the acetone-d3 system.…”

“…High purity was confirmed by gas chromatography and by infrared and nuclear magnetic resonance spectrometry. Azomethane was supplied by Merck, Sharp, and Dohme (Canada) Ltd; the sole impurities were traces of nitrogen, methane and ethane, and these were removed as described previously [5]. Carbon monoxide of 99.99% purity and argon of 99.9995% purity were supplied by the Matheson Company and were used without further purification.…”