Radiolysis of methane. Formation of acetylene

Photochemistry of methane in the photoionization region

“…Because at a methane pressure of 100 torr approximately 50 percent of the excited C ZH4 formed in process 15 were shown to dissociate [23], the low yield of C2H2 in the photoionizationexperiments (tables 1 and 2) rules out reaction 14 as an important mode of neutralization of the C2Ht ion. Proton transfer on the aluminum window surface and/or to H20 desorbed from the wall is a likely explanation for the nearly quantitative conversion of CzHt ions to CZH4.…”

“…The relative rate data given in the last column of the table indicate that reaction of the C 2D 5+ ion with the symmetric molecule, cyciohexane-1,1,2,2,3,3-ds , shows that there is a slight (5 percent) preference for reaction of an ethyl ion at the CH 2 position rather than the CD 2 position C 2D5 + + c-C6H6D6~ C 2D 6 + c-C 6HsDt. (23) Both reactions are exothermic by 35 kcal/mol [311_ It is not surprising that the relative importance of reactions 22 and 23 does not change as a function of the energy of the photons used to produce the C 2 D5 + ions in CD 4• Though the C2Dt ions may be formed with different energy contents in experiments performed at different energies, in these dilute mixtures any excess energy will be dissipated by unreactive collisions with methane before reaction with the additive can occur. The increase in k221k23 which is seen when C 2D 5 + is replaced by C 2 Ht (table 3) is too small to be considered as a genuine isotope effect.…”

“…In the CfL-alkane mixture given in tables I and 2, <I>(C2H6) is approximately equal to the reduction in <I>(C2fL), indicating that in "pure" methane most of the C2Ht ions yield c a as a neutral product. Pulse radiolysis experiments [23] have shown that if the neutralization occurs by electron recombination, acetylene is produced through the following reaction sequence:…”