Rotational effects in broadening factors of fall-off curves of unimolecular dissociation reactions

Abstract

Strong collision fall-off curves of unimolecular dissociation and the reverse recombination reactions are calculated by using the statistical adiabatic channel/classical trajectory model (SACM/CT). This formalism properly accounts for angular momentum coupling of transitional modes with overall rotation. Calculations are made for linear molecules dissociating into linear fragments and atoms with randomly chosen properties of the transitional modes and for isotropic as well as anisotropic potentials. Analytical representations of center broadening factors as a function of molecular parameters are given. A comparison between fall-off curves from rigid activated complex RRKM theory, from the present loose activated complex SACM/CT model, and from CT calculations on an ab initio potential is made for the HO₂ → H + O₂ system. It is shown that, besides rotational effects, energy-dependent anharmonicities of the density of states also influence the shape of the fall-off curves in this system.