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Articles you may be interested inAbsolute rate constants for the reaction of O(3 P) atoms with ethylene, propylene, and propylened6 over the temperature range 258-861 K

This work describes the reactions of the ions C2H5+ and CH5+ with C3D8, C4D10, C5D12, as well as the reactions of C2D5+ and CD5+ with C3H8. It is shown that ethyl ions undergo a hydride transfer reaction with all higher hydrocarbons even though they are present at a concentration of only 0.01%. The scavengers NO and O2 react with ethyl ions effectively, provided the relative concentration of the higher hydrocarbons is less than that of the free radical scavengers. A proton-transfer reaction between CH5+ and higher hydrocarbons followed by a rapid decomposition of the protonated hydrocarbon into a carbonium ion and a neutral alkane molecule is shown to occur. From the data it can be deduced that at a methane pressure of 48 cm G(C2H5+) =0.9±0.2 and G(CH5+) =1.9±0.2. It is concluded that in earlier published studies of the radiolysis of methane, the C2H5+ and CH5+ ions reacted with the accumulated products or with the added free radical scavengers, thus excluding the neutralization of these two species.

The photolysis and radiolysis of equimolar CH4–CD4 mixtures were investigated as a function of pressure. The fact that, in the presence of NO, the ethane fraction consists entirely of C2D6, C2D4H2, C2H4D2, and C2H6 in comparable amounts indicates that CH2 and CD2 are produced. The relative yield of these ethanes which are formed by insertion of methylene into methane increases with pressure in both the photolysis and radiolysis. In the radiolysis, the G value reaches a value of 0.35±0.1 at pressures above 15 atm. Information about the effect of pressure on the production of the ethyl ion was obtained by investigating the radiolysis of CH4–C4D10 and CD4—C3H8 mixtures from 1.5 cm to 130 atm. The data indicate that there is a gradual decrease of the ethyl ion yield with increase in pressure while the parent ion yield increases with increase in pressure to a pressure of at least 15 atm.

The photolysis of CH. and of CH.-CD. mixtures has been investigated at 1236 A (10.0 eV) and at 1048-67 A (11.6-11.8 eV). The excited methane molecule dissociates to form H2, H, CHa, CH2, CH, and probably also C. The CH and CH2 radicals insert into methane to form internally excited C2H.• and C2H6* species, respectively. Below one atmosphere, all C2H. radicals decompose to form C2H., while the ethane molecules are partially stabilized. The relative quantum yield of CH increases about threefold when the wavelength is reduced from 1236 A to 1048-67 A. On the basis of an isotopic analysis of the hydrogen produced in the photolysis of CD.-H2S mixtures, it is concluded that at 1236 A, D atoms constitute at least 65% of the "molecular" deuterium yield. In the radiolysis, ethylene is largely, although not exclusively formed by the insertion of CH into methane. It is demonstrated that addition of small concentrations of an unsaturated hydrocarbon to methane profoundly affects the ion-molecule reaction mechanism and, therefore, does not lead to a dependable value of the "initial" ethylene yield as suggested in earlier studies. Upon application of an electrical field, the production of CH and CH2 is augmented in the saturation current region. The importance of the latter two radicals in the direct and rare-gas-sensitized radiolysis is examined briefly. The formation of hydrogen in the radiolysis will be discussed on the basis of new information derived from CD.-H2S experiments. The production of hydrogen in the radiolysis of Xe-CH.-CD.-NO mixtures has also been reexamined in view of a recent study in which it was asserted that all of the hydrogen in such a mixture is due to the unimolecular decomposition process CH,*->CH2+Hz• Our data disagree with this view and actually demonstrate that CH and CH. play a minor role in the xenon-sensitized radiolysis of methane.