Kinetic Energy Isotope Effects of Bromine Reactions Activated by Radiative Neutron Capture in Gaseous CH<sub>3</sub>F and CD<sub>3</sub>F

Helton, R.W.; Yoong, M.; Rack, E. P.

doi:10.1021/j100682a600

Cited by 5 publications

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“…The isomeric transitions proceed via higjily converted gamma-rays, resulting in multiple positive charged ®®' ®^Br. Both types of experiments require the presence of Br-containing Compounds (e. g. Br2 [ 1,[3][4][5][6][7][8], HBr [9], CHsBr [10]) in macroscopic amounts (0.5-10%). Chemical reactions of recoil Br particles with these Compounds can occur and as their ionization potentials are below that of a Br atom (11.81 eV), also Charge neutralization can take place.…”

Section: Introductionmentioning

confidence: 99%

Chemical Effects of the ^76,77Kr-> ^76,77Br Decay in Fluoromethanes

1984

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The reactions of "Br species -formed by the decay of " ••"Kr -with CHJCF4-X (JC = 0 -4) are studied. From experiments with high energetic recoil Br atoms and from scavenger and moderator effects, it could be deduced that the Br-for-F substitution proceeds via reactions of Er"*" and Br" ions, whereas substitution of H atoms is merely due to reactions of Br"*" ions. The small "Br/"Br isotopic ratio for H substitution is ascribed to differences in the kinetic energies between "Br and "Br. The higher ratios found for F substitution are at least partly due to reactions of "Br" ions. Most of the product yields could be divided in two fractions, formed by reactions of energetic and of thermal Br particles, respectively. Thermodynamic considerations lead to the conclusion that electronically excited Br''" CD^) and Br"*" (' ions are, at least partly, responsible for the energetic F substitution yield. Thermal reactions occur in a gasphase düster and, as most of the reactions of Br" ions are endothermic for CH3F, the thermal yield must be due to reactions of Br"*" ions. Substitution of F atoms is favoured above that of H atoms due to the fact that Br+ ions react primarily with the lone pair electrons of the F atom.

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Section: Introductionmentioning

confidence: 99%

Chemical Effects of the ^76,77Kr-> ^76,77Br Decay in Fluoromethanes

1984

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“…The physical nature of the (n, 7) activated 80m Br species entering organic combinations is not fully understood. In some iliim organic systems, however, (n, 7) activated Br has been shown to react as neutralized atoms with excess kinetic energy [5,6,7]. It is interesting to compare the behavior of recoil tritium atoms with (n, 7) activated 80m Br in the same organic system.…”

Section: Introductionmentioning

confidence: 99%

The Reactions of Recoil Tritium Atoms with Cyclopropyl Bromide

Davanloo

Wai

1973

Radiochimica Acta

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58 P. DAVANLOO and C. M. WAI, The Reactions of Recoil Tritium Atoms with Cyclopropyl Bromide Radiochimica Acta cited intermediate, [CH 2 I*I]*, which underwent extensive unimolecular decomposition, then the correlation of the slopes and intercepts in Fig. 2 to direct and indirect fission yields for 135 1 would not have been the same as for 133 1 and 131 1. The only other way the observed ratios for all three isotopes might have remained constant was if the extent of unimolecular decomposition was fortuitously the same for both types of iodine species. When the large differences in kinetic energy of the directly and indirectly formed iodine isotopes are compared, this last suggestion does not seem very likely. At the present time it is not exactly clear how the indirectly formed iodine isotopes are reacting to form the CH 2 I*I molecules. The calculated recoil energy and the scavenger data of Table 2 rule out the translationally excited and thermal energy atoms respectively. The low recoil energies, the insensitivity of the yields to the Ar concentration and the very nature of the β "-decay event all suggest an ion-molecule reaction. This hypothesis is further supported by the results of a separate series of experiments at high moderator concentrations which used 1,3-butadiene in place of Ar. In this high moderator concentration region, the yield for all three isotopes are significantly lower than the Ar results and extrapolate to a Ρ = 0.0 yield at 1.0 mole fraction 1,3-butadiene. In this context the primary difference between the two moderators is the ionization potentials: Ar, 15.4 ev; I, 10.4 ev; and 1,3-butadiene, 9.1 ev [23], Thus, an I + ion formed via β "-decay might not be neutralized in the Ar system and could react as an ion. However, in the butadiene system, this same ion could be exothermically neutralized and scavenged prior to reacting with a CH31 molecule. ConclusionThe primary point of this report is to show that in an Ar moderated system, the slopes of the yield curves correspond rather closely with the fractional direct fission yields. Likewise the ratios of the yields extrapolated to 1.0 mole fraction Ar could be used to calculate the indirect fission yields. We are currently extending this technique to other systems where the iodine fission yields are either in dispute [24, 25] or have not yet been measured.Abstract Secondary unimolecular isomerization following recoil tritium substitution reactions in gaseous cyclopropyl bromide was investigated. The internal excitation energies in product molecules following T-for-Br and T-for-H substitution reactions in c-CjHjBr are discussed. A comparison of recoil Τ and (n, y) activated 80mg r reac tions with c-C 3 H 5 Br is given. RésuméOn a étudié l'isomérisation secondaire monomoléculaire consécutive aux réactions de substitution fournies par le tritium de recul dans le cyclopropylbromure gazeux. On discute des énergies internes d'excitation des molécules produites par les réactions de substitution du Br par Τ et de l'H par Τ dans le c-C 3 H 5 Br. On ...

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