Large Enhancements in Dissociative Electron Attachment to Chlorine Containing Molecules Adsorbed on H2O Ice
The study of chlorine-containing molecules, especially chlorofluoro-carbons (CFCs), has received continued interest mainly because of their well-known association with the ozone depletion in the Earth’s stratosphere. It was first proposed1 that chlorine atoms are produced by photolysis of such species as CF2C12 (CFC-12) and CFCl3 (CFC-11). For the former species, the reaction is: CF2Cl2 + hv→Cl + CF2Cl. The resultant Cl atom destroys ozone via a (Cl, C1O) reaction chain. The significance of CFCs to the ozone depletion has been well recognized since the discovery of the Antarctic ozone hole.2 Nevertheless, the above photodissociation model predicts a maximum rate of Cl atom production in the upper stratosphere at altitudes of 30∼40 km and a negligible rate below 20 km.1 However, the ozone hole is found at the lower polar stratosphere at an altitude of ∼15 km. It is known that the creation of the ozone hole is closely related to the existence of polar stratospheric clouds (PSCs) that form in the Antarctic stratosphere due to the extreme cold temperature; these PSCs consist mainly of condensed-phase water ice and nitric acid/ice.3,4 The formation of the ozone hole has been attributed to heterogeneous reactions occurring on surfaces of PSC ice particles, which convert chlorine from the inactive compounds (HCl and ClONO2) into reactive Cl2: HCl + ClONO2 → Cl2 + HNO3.3,4 Upon photolysis, Cl2 releases chlorine to destroy O3.
KeywordsRecombination Ozone Helium Chlorine HNO3
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- 9.N. V. Klassen, in Radiation Chemistry: Principles and Applications, ed. by Farhataziz and M. A. Rodgers, (VCH, New Year, 1987), chap.2.Google Scholar