On the mass independent isotope fractionation in ozone

Abstract

The theoretical approach developed by the authors in order to account for the mass independent isotopic fractionation observed in ozone is applied taking into account explicitly the isotopic masses of the reactants and the relative positions of the oxygen atoms in O3. From classical trajectory calculations on the potential surface of Schinke et al. for the collision O+O2⟶O3∗⟶O+O2, a supposed quantum effect is simulated, resulting in different average lifetimes for the intermediate complex when its formation involves collisions between distinguishable or between indistinguishable isotopes. The stabilization of the complex by a third body MO3∗+M⟶O3+M is assumed to involve only the inelastic collisions. Under this assumption, we show that the effect of indistinguishability, the ΔZPE correction, and by taking into account the explicit masses of the reactants, reproduce (in the order of importance) the experimental results within ±2%. An alternative definition of the lifetime of the complex reduces the number of apparently free parameters in the calculations.