Reactions of 2.8-eV Tritium Atoms with Methane

Abstract

Tritium atoms with 2.8-eV kinetic energy have been formed by 1849-Å photolysis of TBr, and have been reacted with CH4 in the presence of Br2. In addition to HT from the abstraction reaction known in thermal systems, the direct substitution of T for H to form CH3T has been observed. The ratio of HT/CH3T is 3.6 to 4.0 in low Br2 mole fraction. In Br2 mole fractions exceeding 0.5, this ratio is reduced to 3.0, and the absolute yields of both HT and CH3T are greatly reduced. The formation of HT and CH3T from hot reactions of T with CH4 competes with the hot reaction of T with BR2 to form TBr.

Resonant features in the energy dependence of the rate of ketene isomerization

“…1͒. ͑This isomerization or exchange process was also deduced from much earlier ''hot atom'' experiments by Rowland et al͒ 2 From the branching ratio between normal and exchanged products, Lovejoy and Moore used a simple kinetic model to extract separately the unimolecular rate constants for direct dissociation ͑i.e., H 2 CϭCЈϭO→H 2 CϩCЈϭO without isomerization͒ and for isomerization, k d (E) and k iso (E), respectively. In a series of articles, 3 Moore et al have reported on many other interesting aspects of ketene photodissociation that are not the subject of the present article.…”

A New Approach to Some Aspects of Recoil Tritium Chemistry

“…To estimate the qualitative effect of this collisional dissociation on the HT yield in gas phase recoil tritium moderation studies, the HT produced in the computer simulated reaction, (1), was allowed to collide with rare gas atom until either it had dissociated or its total energy 1.0 Ρ 0.6 ' HT 0.2 8 16 32 eV 64 Translational energy Fig. 8.…”

“…and K. it can be seen that this implied that HT was formed, in the main, at lower average energies than RT [1, 2], This was not an unexpected finding since Η-abstraction was known to have a lower threshold than H-substitution [8], and indeed was the only process observed at thermal energies.…”

“…Thus it was interesting when quite large scavenger effects were observed with bromine and iodine in systems moderated by moderators other than helium [23, 24], Since it is unlikely that recoil tritium atoms could react with these scavengers at energies much above the T-Br bond strength, it is apparent that a large scavenger effect on the H-abstraction yield is not consistent with the formation of large amounts of HT by high energy processes [23]. However, such an effect was observed and one is tempted to cite this as evidence in support of the "energy cut-off model", especially since a similar variation in the abstraction yield has been observed for reactions by 2.8 ev tritium atoms [8].…”

“…At one time it seemed that a general agreement on the nature of recoil tritium reactions with simple molecules was within easy reach [5], However, in recent years a number of experimental results have been reported which have led to considerable disagreement and confusion. The situation was further complicated by conflicting theoretical predictions [6,7], based on calculations of varying degrees of approximation, and by studies of reactions of photolytically generated tritium [8] and deuterium [9] atoms.…”