ClOOCl (ClO dimer) photolysis is believed to dominate the catalytic destruction of polar stratospheric ozone during springtime through the production of atomic chlorine. Decomposition by an alternate pathway to form ClO would not catalyze ozone loss. Molecular beam experiments have demonstrated that photoexcitation of ClOOCl at both 248 and 308 nm leads to dissociation via multiple dynamical pathways, producing ClO + ClO and 2Cl + O 2 . At 248 nm, both concerted and sequential dissociation to 2Cl + O 2 were observed. The primary dissociation channels occurred within a rotational period at both excitation wavelengths. The relative Cl:ClO product yields are 0.88:0.12 and 0.90:0.10 at 248 and 308 nm, respectively. Lower limits on these ratios were determined. These results substantially confirm the importance of ClOOCl photolysis in catalyzing springtime polar ozone depletion.) 108.4 kJ/mol (7)

Molecular beam–surface scattering experiments have been used to study the mechanisms of material removal when a hydrocarbon polymer surface erodes in the highly oxidizing environment of low Earth orbit or in a simulated space environment on Earth. During steady-state oxidation, CO and CO2 are produced. Formation of these volatile species is believed to account for a significant fraction of the mass loss of a polymer that is under atomic-oxygen attack. The rate of production of CO and CO2 is dramatically enhanced when a continuously-oxidized polymer surface is bombarded with Ar atoms or N2 molecules possessing translational energies greater than 8 eV. The yield of volatile products from the surface appears to increase exponentially with the collision energy of the inert atoms or molecules. Collisions of energetic inert species may accelerate the erosion of polymers in some exposure environments (e.g. in low Earth orbit, where N2 may strike oxidized surfaces with collision energies greater than 8 eV, and in certain atomic-oxygen test facilities that subject oxidized surfaces to bombardment by O2 molecules with average translational energies of approximately 10 eV).

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