Alkyl Radicals R

The only fate of alkyl radicals in air is reaction with 02:

For the case where R is a methyl group, the reaction is in the falloff region at f atm, and for C2H5, it is close to the high-pressure limit. For C3H7 and above, a value for the effective second-order rate constant, k^, of ~(0.8-2) X 10"" cm3 molecule"1 s"1 means that the lifetime of an alkyl radical at ~ 1 atm in air is ~ 10 ns.

A second possible channel, in which the alkene and H02 are formed from decomposition of the excited RO* intermediate before it is stabilized, is very small; thus, this channel is < f% for C2H5 + 02 (C2H502)* -ยป C2H4 + H02 and < 0.13% for C3H7 + 02~-> (C3H702)* -> C3Hft + H02 at f atm pressure and room temperature but becomes important at higher temperatures, e.g., in combustion systems (Kaiser, 1995; Benson, 1996; Kaiser and Wallington, 1996a).

0 0

Post a comment