Classical and quantal contributions to the mechanisms of ion–molecule reactions. Chemistry of O +2

Abstract

A semi-classical qualitative model is developed to predict the nature of collision complexes for thermal reaction of O⁺₂ with neutral substrates. The initial geometry of this complex is assumed to be determined by the classical potentials of the system. Only the frontier orbitals of the two species which can overlap in this classical orientation then need to be considered in the rationalization of the initial progress of the chemical reaction. The model is further simplified by the use of the united atom model to characterize the frontier orbitals of the reacting species. It also leads to an analogy between O⁺₂ and d block transition metal ions. The abundant data on the geometry and bonding of the substrates of interest with metal ions can then be directly compared to the nature of the gas phase complexes of O⁺₂. In one case the geometry predicted in this way has been observed from a previous semi-empirical m.o. calculation. The model is applied qualitatively in the interpretation of the kinetics of gas-phase reactions involving O⁺₂ and O₂, N₂, NO, NH₃, H₂O, CH₄ and N at 300 K.