Structural and temperature effects on Cl− yields in electron-induced dissociation of CF2Cl2 adsorbed on water ice

The temperature (T) dependence of the Cl− yield in the electron-stimulated desorption (ESD) of a submonolayer of CF2Cl2 adsorbed on amorphous H2O ice grown at 25 K exhibits a peak between 50 and 70 K. This peak and a sharp drop in electron-trapping coefficient of ice near 50 K show strong evidence for a phase transition. The peak disappears for CF2Cl2 on crystalline ice; instead, a non-Arrhenius Cl− dependence on T is observed with a critical temperature of ∼224 K. The peak is also not pronounced in the T dependence of the ESD H− yield of amorphous ice, which involves no transfer of trapped electrons.