Hydrogen abstraction reactions by atomic fluorine. IV. Temperature dependence of the intermolecular kinetic isotope effect for the nonthermal 18F+H2 reaction

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Abstract
The nuclear recoil systems 18F vs H2/C3F6 and 18F vs D2/C3F6 were investigated from 273–347 °K over the full range of mixture compositions at a constant pressure of 1000 Torr. The results were systematized and interpreted within a nonthermal bimolecular rate constant framework. The phenomenological rate constants as well as their purely non‐Boltzmann components exhibited significant composition and ambient temperature dependences. Most, if not all, of this latter effect was attributable to the 18F*+C3F6 reaction channel, either through an internal state coupling mechanism or through secondary decomposition of excited CF3ĊFCF218F radicals by 18F‐atom loss. Preferred values for the thermal reaction fractions in extrapolated pure H2 (or D2) and C3F6 systems were 20±10% and 20±20%. The corresponding average intermolecular kinetic isotope effect for the pure non‐Boltzmann 18F+H2 reaction was 1.3±0.1.