6533b7d5fe1ef96bd1264321

RESEARCH PRODUCT

Quantum dynamics of the oxygen isotopic exchange : lifetimes of metastable states of the ozone intermediate complex

subject

description

This thesis aims to describe the ozone dynamics during the isotopic exchange reactions of oxygen of type xO + yO zO (xO yO zO)* xO yO + zO, where x, y and z are the atomic masses of the stable oxygen isotopes (16, 17, 18). Firstly, we analyze several methods of accurate description of the atom interactions and numerical schemes to obtain the observables for the collision. Then, in a full-quantum hyperspherical formalism, we study the actual dynamics of the reactive process O + O2 -> O3* -> O2 + O. The metastable ozone created can then either decompose into oxygen by the inverse reaction, or relax into stable ozone by exchanging energy with the environment, typically N2 or O2 molecules. These two processes are in competition and play a key role in the mass-independent fractionation (MIF) of ozone in the stratosphere, first observed in 1981. The lifetimes of the O3* metastable complex are computed for any total angular momentum J, using the Smith matrix calculated alongside the scattering matrix within an efficient numerical propagation scheme. This algorithm was written and implemented in the HYP3D code base during the thesis before being used for the aforementioned collision. We show the apparition of a quasi-continuum of O3* metastable states, all potentially leading to stable ozone via environment driven stabilization. We confirm, within a full dynamical description, a trend previously suggested by other groups based on completely different approximate methods. We also demonstrate the absolute necessity of taking the high J values into account during calculations to rigorously describe the actual ozone dynamics in the stratosphere. Finally, we review some stereodynamical computations we made to shed light on the vectorial aspects of the oxygen exchange reaction. Numerous parameters are analyzed to conclude that a lot of relative orientations of the reactants are indeed possible, but that their respective probability strongly depends on the kinetic energy or the internal state of the reactants.