THE INFLUENCE OF HINDERED ROTATIONS ON RECOMBINATION DISSOCIATION KINETICS/

The variational canonical flexible transition state theory expressions for the thermal reaction rate constant are reviewed and then applied to the barrier-less recombination reactions H + CCH, H + CF3, and CH H-2. The rate constant expressions can classically accommodate any de scription of the hindering potential governing relative orientation ch anges between the reactants at a given distance. The distance held fix ed during the relative orientation changes can be fully optimized. The three applications display comparable and large variations between th e harmonic oscillator and free rotor limits of the hindering potential . The actual hindering potentials are all derived from similar ab init io electronic structure calculations. With these potentials, the rate constant for H+CF3 is somewhat free-rotor like, the rate constant for CH+H-2 is mostly harmonic-oscillator like, and the rate constant for H +CCH is largely in between these two limits.