Isotopic and Dynamic effects in Excited Ozone: symmetry breaking, high-energy states and dissociation – IDEO

The main goal of this project is the understanding of ozone formation and decomposition with a particular insight into their isotope dependence. The formation of ozone proceeds mainly through the O2+O -> O3* chemical recombination reaction. The ozone metastable sates, O3*, can be stabilized into bound rovibrational vJK-states by collisions with a third body (M): O3*+ M -> O3(v1,v2,v3,J,K) + M. According to the commonly accepted mechanism, electronic potential energy is converted into internal energy during ozone formation, leading to the large population of highly excited vibrational states, close to the dissociation limit. The reactions above are the principal ozone formation mechanism at nearly all altitudes in the atmosphere, and probably the only significant source in the stratosphere. It is known that a significant fraction of energy released in the recombination reaction leads to ro-vibrational excitations, but experimental information on metastable and very highly excited ro-vibrational states on the ozone ground state potential energy surface (PES), which are different for various isotopic species, is completely missing. In contrast, the lifetimes of resonance states near dissociation have been theoretically calculated. These quantum calculations, yet limited to J=0 rotational numbers, already indicate an extremely strong dependence on individual isotopic combinations in the above reaction. The central and original aspect of this proposal is the importance given to the symmetry breaking by isotopic substitution, the open state configuration of the ozone main isotopologue being of the C2v symmetry while heteronuclear species can be either of C2v or Cs symmetries. We propose advanced experimental studies and theoretical calculations on ozone quantum states near dissociation, on the coupling of vibrational modes through accidental resonances, and on symmetry-breaking effects related to isotope substitution in order to give key insights into the various aspects of the complex kinetics of dissociation and recombination of ozone. This requires an improvement of knowledge in various related fields: new data on excited vibrational states via ultra sensitive spectroscopic experiments, accurate and global Potential Energy and Dipole Moment Surfaces taking into account non-adiabatic interactions, dynamical experiments and calculations. The consortium of three complementary partners at Reims, Grenoble and Paris proposes the study of isotope effects via a concerted program of new and complementary quantum calculations and experiments on ozone excitation, absorption, photodissosiation and thermal decomposition. The working program may be subsumed under the following three strongly interrelated research actions, combining experimental and theoretical work: 1. Experimental determination of highly excited quantum states near the dissociation limit including Cavity Ring Down Spectroscopy up to 95 % of the dissociation energy and double resonance experiments accessing highly excited 'dark' states undetectable through direct absorption. These measurements will provide the experimental basis and validation for: 2. Advanced electronic structure and rovibronic energy level calculations, potential surfaces and non-adiabatic effects, which in turn will be used to access the dynamical dimensions of the problem, which are investigated by: 3. Absorption cross section measurements, experiments on ozone decomposition and photo-dissociation, and theoretical calculations of the excited state dynamics of various isotopologues By addressing fundamental questions of the quantum physics of excited ozone, our proposal strives to make a significant contribution to world-wide long term efforts in utilizing and exploring the yet puzzling isotope effects in ozone, which not only are poorly understood, but also have a tremendous impact on applied science fields, such as on atmospheric and climate research, for instance. The underlying idea is to investigate a very specific molecular system with diverse approaches in a broad range of theoretical and experimental techniques. Recent experimental and theoretical advances, put forward by individual project participants, will allow studying and quantifying the molecular physics of ozone just up to the dissociation threshold of the molecule, which is the most relevant energy region for dynamic processes. By accounting for essential but not yet sufficiently studied features (non-adiabatic interactions of electronic states, symmetry breaking effects, impact of quantum rotational structure and resonances) through advanced calculations and measurements, it will be possible to develop a more complete and realistic description of the ozone dynamics. The proposal is based on unique expertise and experimental set-ups, where the respective partners are recognized on the international level and where the French research teams have recently demonstrated their innovative character.