Hydrogen abstraction reactions by atomic fluorine. V. Time-independent nonthermal rate constants for the /sup 18/F+H/sub 2/ and /sup 18/F+D/sub 2/ reactions

The general time-independent collision theory formulation for the bimolecular rate constant has been adapted for the description of hot atom systems. Two types of hot atom energy distribution functions have been considered in an application to the /sup 18/F+H/sub 2/ reaction system: (i) a delta-function distribution, and (ii) a steady-state Maxwellian distribution characterized by a hot atom temperature T/sub A/. From the time-independent solution of the Boltzmann equation together with microscopic reactive cross sections determined from quasiclassical trajectory computations, nonthermal /sup 18/F+D/sub 2/ processes. The results showed little sensitivity to the assumed shape of the hot atom energy distribution or to the magnitude of the barrier height along the reaction coordinate. The intermolecular kinetic isotope effect kappa/sub H/2/kappa/sub D/2 provided a sensitive probe of the average energy of hot reaction, suggesting an average /sup 18/F laboratory kinetic energy of 50 +- 10 eV for the /sup 18/F+H/sub 2/ process under nuclear recoil conditions. (AIP)