No abstract

The yields of HT from "hot" abstraction reactions by energetic tritium atoms reacting with various substances RH have been measured in a large excess of C2D •. The energetic tritium atom fluxes are reasonably similar in such systems and permit comparison of absolute HT yields from different R-H bond types. A more accurate comparison is possible when the HT yields are normalized to the yields of either the hot abstraction or substitution reactions with C2D •. The hot HT yields so measured from hydrocarbons show an excellent correlation with the bond-dissociation energies of the C-H bonds involved, with higher yields from weaker bonds. The abstraction of H from CDaCH2CDs was favored by approximately 1.4, per bond, over H from CHaCD2CH3• No significant differences were observed in the DT/C2D3T ratios from reaction with C2D. in the various mixtures with different substances. A preference of 1.27 ±0.02 was observed for the abstraction of H from C 2 H. vs D from C2D •. No isotopic molecule difference was observed between the energetic addition reaction of tritium atoms to the olefinic position in C2H. vs C2D •. 5

The intermolecular kinetic isotope effect for the title reaction has been investigated using a moderated nuclear recoil technique. The following Arrhenius temperature dependence was obtained: kH2/kD2 = (1.04±0.06)exp[(382±35)/RT]. This result is in quantitative agreement with an independent study based upon a discharge flow reactor method. The advantages and limitations of the nuclear recoil procedure are considered, and relevant literature results are critically reviewed.

Nuclear recoil 18F reactions in CH3CHF2 have been investigated throughout the effective pressure range 0.3–190 atm. The principal reaction channel is F-to-HF abstraction for which the combined yield from quasithermal and energetic processes in the presence of 5 mole% H2S additive is 83.4%±0.2%. A reaction mechanism is proposed that involves the organic product forming channels F-for-F, F-for-αH, F-for-βH, F-for-ĊH3 and F-for-ĊHF2. The results are compared with those reported for the 18F+CH3CF3 system.