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 18F+H2 reaction system: (i) a δ-function distribution, and (ii) a steady-state Maxwellian distribution characterized by a hot atom temperature TA. From the time-independent solution of the Boltzmann equation together with microscopic reactive cross sections determined from quasiclassical trajectory computations, nonthermal 18F+D2 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 κH2/κD2 provided a sensitive probe of the average energy of hot reaction, suggesting an average 18F laboratory kinetic energy of 50±10 eV for the 18F+H2 process under nuclear recoil conditions.
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Semicontinuum model for the trapped dielectron in polar liquids and solidsA semicontinuum model is applied to trapped electrons in glassy ethanol at 77°K. The configurational stability of the ground state has been established. Ground, excited, and continuum states are calculated self-consistently for specific orientations from 80° to 0° of the molecular dipoles with respect to the trapped electron. It is shown that the spectral shifts observed for trapped electrons in pulse radiolysis experiments on alcohol glasses and the shifts observed upon warming from 4 to 77°K after 'Y irradiation at 4°K can be semiquantitatively accounted for by the molecular dipole orientation mechanism. The cavity radius of the trapped electron also increases somewhat upon dipole orientation but this is a small effect. The effect of dipole orientation upon other physical properties of the trapped electrons in ethanol is also discussed.
A model is developed to treat the binding energy of excess electrons in nonpolar liquids and solids such as alkanes. Interaction of the excess electron with C–H bond dipoles is considered for several geometrical arrangements. On this basis it is found that a binding energy of about 0.5 eV can be explained for trapped electrons in condensed alkanes. Although long range polarization interactions are unimportant, the electron interaction with the bond microdipoles of a net nonpolar molecule appears to be the key to understanding electron binding in alkane matrices.
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