Research Articles

The "Ozone Deficit" Problem: O2(X, v ≥ 26) + O(3P) from 226-nm Ozone Photodissociation

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Science  23 Sep 1994:
Vol. 265, Issue 5180, pp. 1831-1838
DOI: 10.1126/science.265.5180.1831


Highly vibrationally excited O2(X3σg, v ≥ 26) has been observed from the photodissociation of ozone (O3), and the quantum yield for this reaction has been determined for excitation at 226 nanometers. This observation may help to address the "ozone deficit" problem, or why the previously predicted stratospheric O3 concentration is less than that observed. Recent kinetic studies have suggested that O2(X3σg, v ≥ 26) can react rapidly with O2 to form O3 + O and have led to speculation that, if produced in the photodissociation of O3, this species might be involved in resolving the discrepancy. The sequence O3 + hv → O2(X3σg, v ≥ 26) + O; O2(X3σg, v ≥ 26) + O2 → O3 + O (where hv is a photon) would be an autocatalytic mechanism for production of odd oxygen. A two-dimensional atmospheric model has been used to evaluate the importance of this new mechanism. The new mechanism can completely account for the tropical O3 deficit at an altitude of 43 kilometers, but it does not completely account for the deficit at higher altitudes. The mechanism also provides for isotopic fractionation and may contribute to an explanation for the anomalously high concentration of heavy O3 in the stratosphere.