Radiation Chemistry of CF2Cl2: Implications for the Ozone Hole?

Nozomi Nakayama
Wellesley College

We have studied the low-energy electron-induced reactions of dichlorodifluoromethane (CF2Cl2), commonly known as CFC-12, because of a newly proposed hypothesis [1] which suggests that low-energy electrons from cosmic rays, rather than UV-VIS photons from the sun, interact with chlorofluorocarbons to produce chlorine atoms that destroy ozone in the Antarctic. Our experimental procedure involves low-energy (10 – 100 eV) electron irradiation of nanoscale thin films (~ 10Å thickness) of CF2Cl2 grown at 100 K on a molybdenum single crystal in an ultrahigh vacuum chamber (p ~ 1 x 10-10 Torr). Post-irradiation temperature programmed desorption experiments were used to identify several products such as C2F2Cl4 that form via C-F bond cleavage during radiolysis but not photolysis of CF2Cl2. This finding may provide a direct method to verify the role, if any, of cosmic rays in the formation of the ozone hole. The radiolysis product yield as a function of electron energy, electron fluence, and film thickness was also investigated to probe the electron-induced reaction mechanism(s).