Reactions of atomic oxygen (1D) with methane and ethane

Abstract

Gas-phase reactions of 0(1D) with CH* and with C2He were studied by the photolyses of N2O-CH4 and N2O-C2H6 mixtures using 1849-Á light. Pressure effects and radical scavenging techniques were used to identify the sources of the products. At low pressures, where stabilization of excited alcohol intermediates did not occur, the main path of the Oí1!)) + CH4 reaction was to form CH3 + OH radicals, which ultimately produce C2H6. Molecular elimination giving H2 + CH2O occurred to the extent of 9%, which is the same as when the reaction takes place in liquid Ar at 87°K. The main path of the Oí1D) 4-C2H6 reaction was to form C2H5 + OH and CH3 + CH2OH radicals, which ultimately produce n-C4Hio, CsHs, and ChHe as principal products. The total reaction does not proceed via ROH* intermediates. The OH radicals are produced both by fission of such intermediates and by direct abstraction of H atoms, in agreement with the results of Cvetanovic and coworkers. Comparison with previous results in liquid argon indicates that the condensed medium suppresses the abstraction reaction in favor of the insertion reaction. The molecular process giving CH2O + H2 also does not involve the CH3OH* intermediate, asshown by the fact that this path contributes equally both in the gas and liquid phases. (1) This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. NAS 7-100, sponsored by the National Aeronautics and Space Administration. (2) (a) M.

Stabilization of the primary products of atomic oxygen (1D) reactions with carbon monoxide, carbon dioxide, methane and other hydrocarbons in cryogenic matrixes

“…The gas-phase kinetics of O(lD) reactions with numerous molecules such as H2, CO, COz, CHI, and various saturated and unsaturated hydrocarbons have been studied in detail, chiefly by CvetanoviC and co-workersl-s and also by DeMore and coworkers. 6 Three major reaction pathways have been proposed2 for the interactions of O(1D) with hydrocarbons in the gas phase, namely, (1) exoergic C-H bond insertion to form a highly energized alcohol intermediate which, depending on its complexity and the bressure a t which the reaction takes place, may be stabilized or decompose by fragmentation to form radical products, (2) H atom abstraction to give direct formation of alkyl and hydroxyl radicals, and (3) elimination of Hz. Recent dynamics studies of O(lD) reactions with CHI have shown that only atomic hydrogen is formed in the gas phase,' suggesting that the observation of molecular hydrogen in earlier gas-and solutionphase work may be due to hydrogen atom abstraction or recombination reactions.…”

Infrared multiphoton absorption and decomposition of ethanol vapour

“…Three chemical activation studies produced C2H50H in vibrationally excited states and the subsequent decomposition of these provides insight into the decomposition channels of ethanol. The first of these studies involves the insertion of O('D) atoms into a C-H bond of C2H6 to give C2H50H with excess vibrational energy of about 607 kJ/mol, and studies in several laboratories (14,15) found products that could be entirely accounted for by the reactions of free radicals resulting from channels [2] and [5]. Tsang (12) compared these results with theoretical calculations that predicted rate constants for reactions [ I.…”

Thermal stability of alcohols

“…= 389.1 f 4.2 kJ. Cvetanovic and coworkers [5] and Lin and DeMore [6] have determined the life times of various vibrationally hot alcohols formed via the insertion of O(l0) into the C-H bond in appropriate hydrocarbons. R R K M calculations [7] will provide a means of relating the thermal and chemical activation results.…”