STRUCTURES, RELATIVE STABILITIES, AND VIBRATIONAL-SPECTRA OF ISOMERS OF CL2O2 - THE ROLE OF THE CHLORINE OXIDE DIMER IN ANTARCTIC OZONE DEPLETING MECHANISMS

Quantitative ab initio molecular orbital calculations have been applied to the description of the structures, relative stabilities, and vibrational spectra of isomers of Cl2O2. The highest level of calculations performed (MP2/6-31+G (3d)//MP2/6-31G*) suggests that C2 symmetry ClOOCl (chlorine peroxide) is the lowest energy form but that the hypervalent, Cs symmetry species ClClO2 (chloryl chloride) is only about 1 kcal/mol higher in energy. A third form, C1 symmetry ClOClO (chlorine chlorite), lies higher in energy by 7 kcal/mol. Intense infrared absorption bands above 450 cm-1 are predicted by MP2/ 6-31G*//MP2/6-31G* calculations at 765, 679, and 633 cm-1 for ClOOCl, at 1351, 1190, and 490 cm-1 for ClClO2, and at 1275 cm-1 for ClOClO. The theoretical results are compared with experimentally determined thermochemical and vibrational data, and the role of the chlorine oxide dimer in Antarctic ozone depleting mechanisms is discussed.