Photochemical production of alkyl and alkoxyl radicals and their reactions with oxygen

Abstract

The flash photolysis of a series of alkyl nitrites, halides and nitro compounds has been studied using the technique of kinetic spectroscopy in the vacuum ultra-violet region. During the flash photolysis of methyl nitrite, a new transient absorption spectrum consisting of three diffuse bands with centres at 2064, 2036, 1999A, was observed. The spectrum has been assigned to the CH30* radical, which must be produced in the initial photolytic breakdown according to h v CH30NO +CH30*+NO.Experiments using the higher members of the homologous series of nitrites failed to detect any spectra assignable to other ROO radicals, but data regarding their stability have been obtained. On the basis of their reactions with oxygen it has been possible to classify the alkyl nitrites as follows : (a) those containing the -CH2ONO grouping and which react rapidly with oxygen, giving an intense OH spectrum; (b) those not containing this grouping and which do not react with oxygen to give OH.In the experiments with alkyl halides and nitroalkanes the only spectrum attributable to an alkyl radical was that of methyl. In some cases the methyl resulted from the break-up of higher alkyl radicals. A study was made of the stability of these radicals and of their reactivity with oxygen. The primary processes involved in the photochemical decomposition of all three classes of compound are discussed, together with the effect of inert diluent gases on their reactions with oxygen.

Mechanisms of formation of sulfur oxides in combustion

“…Merryman (1965a, 1967) applied the flame microstructure technique to derive the kinetics and mechanisms of some of the high temperature oxidation processes, while Bradley and Dobson (1967) studied the high temperature oxidation of H.S in shock waves. McGarvey and McGrath (1964), using the flash photolysis technique, and Marsden (1963), employing mass spectrometric techniques, have identified and further confirmed the presence of several intermediates in the H>S oxidation mechanism.…”

“…McGarvey and McGrath (1964), on the other hand, offer specific evidence for the SO radical in the photolytic oxidation of H2S. Using the flash-photolysis technique, they observe a spectrum for SO in the ultraviolet region of 2400 to 1900 Á.…”

“…The S02 spectrum is noted to give way to a continuum and to reappear as the continuum disappears. McGarvey and McGrath (1964) assign a transient spectrum in the range 1840-1740 A to SOO. Levy and Merryman (1965a,b) observed "excess" SO, values in mass-spectrometric analysis of SO, produced in the H,S flame which may or may not have been associated with the superoxide.…”

Multiphoton Ionization and Dissociation of Nitromethane Using Femtosecond Laser Pulses at 375 and 750 nm

“…The photochemistry of nitromethane (CH 3 NO 2 ) has been extensively studied for many years − principally because the molecule is an important prototypical energetic material. Its ultraviolet absorption spectrum consists of two bands: a weak band around 270 nm with very little absorption strength at wavelengths longer than 350 nm and a very much stronger band at about 198 nm .…”

Excited Electronic States of the Cyclic Isomers of O3 and SO2

“…The minimum energy geometry is bent, but the existence of a low-lying SO 2 isomer was first suggested as an explanation for the strong continuous absorption band which resulted from flashinitiated explosions of H 2 S, CS 2 , and COS. [29][30][31] Assuming that the molecule responsible for the absorption band was a direct precursor to SO 2 , many investigated the possibility of a superoxide (S-O-O) isomer. 29,32,33 Influenced by the studies of Shih et al 8 on cyclic-O 3 , the possibility of a low-lying ring isomer of SO 2 began to be investigated. 23,[34][35][36][37] Kellogg et al found that all three SO 2 isomers were minima at the MRCI level of theory.…”