Rates of chemical reactions dominated by long-range intermolecular forces

Abstract Some simple theories are described for calculating rate constants for neutral chemical reactions in the gas phase which are dominated by long-range forces and have no barriers in the potential energy surface. The methods involve combining an adiabatic capture approach with the quantum mechanical sudden approximation of non-reactive energy transfer. A version of the technique is shown to work well in calculations on the O + OH reaction. The methods are applied to the diatom-diatom reactions SO + OH, NO + BrO, NO + ClO, CN + O2 and CH + O2. The results provide new information on the origin of the negative temperature dependence of the rate constants for reactions such as these.