Ethane, dissociation photolysis

By comparison, the photolysis of Me4Ge with an argon fluoride laser at 193 nm yields trimethylgermane, ethane, methane, ethylene and layers of Ge as the end products209. These results have been interpreted as indicative of electronically excited Me4Ge undergoing preferential molecular elimination (equations 37a and 37b) over the dissociation shown in equation 36. 

The photolysis of pure methane in the solid phase and of methane in argon or krypton matrices has been examined by Ausloos et at 1236 A. The photolysis of solid methane is very similar to the gas-phase photolysis. Hydrogen and ethane are the major products, with CH4-CD4 mixtures showing an H2 and D2 richness over HD, and a predominance of d, d, d and rfg fractions in ethane. These features are indicative of molecular elimination of hydrogen followed by insertion of CH2 into methane. It was found that the smaller but significant contribution of ethane- s was greater than that of either ethane- i or d. This has been interpreted as evidence for the primary photolysis of methane into a hydrogen atom and a methyl radical. The fact that little ethane- i or is found excludes the formation of the methyl radicals by the dissociation of a hot ethane molecule after insertion by CH2. The minor products of photolysis are ethylene, propane, butanes, propene and pentanes. The presence of ethylene-[Pg.68]

The earliest studies of the photolysis of ethane suggested that the dissociation of ethane to two methyl radicals and to an ethyl radical and a hydrogen atom were the primary steps of the process. The more recent work has shown that the photolysis is much more complicated, with several primary steps involved. As a basis for discussion the following reaction scheme is used. 

Recent investigations on ethane formation in the photolysis of acetaldehyde indicate that decomposition into methyl and formyl radicals occurs from the triplet state which is also removed by first-order internal conversion and, to some extent, by second-order deactivation. In the mercury-photosensitized reaction methyl radicals are formed by direct dissociation of the excited aldehyde molecules, as well as by collision of excited mercury atoms . 

The occurrence of this reaction sequence is further substantiated by the observation that adding nitric oxide in the photolysis experiments does not change ethylene-acetylene yields (Table IV). Evidence for the analogous process in ethyl iodide involving elimination of HI has been presented in previous photolysis studies (23, 34). The ethane product observed in the present photolysis study must certainly be formed by the reaction of ethyl radicals which presumably result from another primary dissociation process,... 

Since no butane is observed as a photolysis product, and since the accepted value for the ratio of rate constants for disproportionation to combination reactions for ethyl radicals is 0.12 (45), ethyl radical interactions may be ruled out as a source of ethane. Therefore, the ethane probably arises from an abstraction reaction following the initial dissociation,... 

Maricq and Szente (1995) used time resolved IR and UV spectroscopy to study the photodissociation of CF3C(0)C1 in photolysis at 193 and 248 nm. They concluded that the net reaction shown by process (III) described the results best rapidly dissociating CF3CO and/or COCl radicals presumably were present as intermediates. At 193 nm the CO is formed with extensive internal excitation (TVib = 3, 800 900 K), whereas at 248 nm it is formed predominantly in v = 0. Quantum yields of the photodecomposition were measured by comparing yields of HCl (formed in experiments with added ethane) and RO2 (experiments with added O2) from CF3C(0)C1 to those from the photodisssociation of CH3CI at 193 nm and CI2 at 248 nm they assumed the latter two species have unit photodissociation efficiencies. Values of the total quantum yield of photodecomposition, ((/>i -t- + < ) = 1.10 0.11 at 193 nm and 0.92 ... 

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