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

Strong collision fall-off curves of unimolecular dissociation and the rever se recombination reactions are calculated by using the statistical adiabati c channel/classical trajectory model (SACM/CT). This formalism properly acc ounts for angular momentum coupling of transitional modes with overall rota tion. Calculations are made for linear molecules dissociating into linear f ragments and atoms with randomly chosen properties of the transitional mode s and for isotropic as well as anisotropic potentials. Analytical represent ations of center broadening factors as a function of molecular parameters a re given. A comparison between fall-off curves from rigid activated complex RRKM theory, from the present loose activated complex SACM/CT model, and f rom CT calculations on an ab initio potential is made for the HO2 --> H + O -2 system. It is shown that, besides rotational effects, energy-dependent a nharmonicities of the density of states also influence the shape of the fal l-off curves in this system.