The effect of the isotopic composition of oxygen on the non-mass-dependent isotopic fractionation in the formation of ozone by discharge of O_2

Abstract

The oxygen gases in a fused silica container cooled to 77K at pressures of 0.5 to 15 cm Hg were energized by an RF generator of 60 kHz to produce ozone which condensed on the cold wall. The isotopomeric compositions of the initial O_2, the O_2 remaining after the discharge, and the O_2 which was completely converted from the O_3 were measured. Oxygen gases of three different isotopic compositions were used. In addition, oxygen pressure, degree of ozone formation, and geometry of the discharge were varied. The isotopomeric data of O_2 gases after the discharge reactions showed very unusual patterns. These patterns depend mainly on the isotopic composition of the oxygen used for the reaction. We compared the data with a model based on the effect of the anharmonicity and the symmetry of the excited ozone molecules on their predissociation. The anharmonicity and symmetry effects depend on the isotopic composition of the O_2 which in turn control the isotope fractionation associated with the formation of ozone. Our data are not compatible with several models such as self-shielding and the structural symmetry of the initial oxygen gas.

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