The steric factor in transition state theory and in collison theory

For thermal reactants, it is shown that classical transition state theory and collision theory yield the very same explicit expression for the steric factor in terms of the 3N - 7 internal coordinates dependence of the barrier to reaction. Various special cases are worked out for an atom-diatom exchange reaction. The original result of Pelzer and Wigner (Z. Physik. Chem. B 15 (1932) 445) is recovered. It is argued that the predicted increase of steric factor with temperature is more realistic than the naive transition state result which can be taken to suggest that it declines. The argument that curvature in Arrhenius plots at higher temperatures is due to steric effects is derived on analytical grounds.