The role of low-energy electrons in the high-energy radiolysis of condensed CF₃I

Abstract

The dynamics of electron-induced reactions in condensed trifluoroiodomethane (CF3I) were studied under ultrahigh vacuum conditions. Seven CF3I radiolysis products (C2F6, C2F5I, C2F3I, CF2I2, C2F4I2, CFI3 and C2F3I3) were identified using temperature-programmed desorption experiments conducted after irradiation with 4 eV electrons. Although C2F6 formation at energies above 4 eV is ascribed to electron-induced electronic excitation followed by prompt dissociation of the C-I bond to form [Formula: see text] radicals that dimerize, the formation of the other six radiolysis products at low sub-ionization incident electron energies is attributed to dissociative electron attachment (DEA) because of the observed resonance peaks in the radiolysis product yields as functions of incident electron energy (∼2 to ∼ 7 eV). All seven CF3I electron-induced reaction products were also identified following irradiation with 500 eV electrons. While dissociative electron attachment and/or electron impact excitation may play an important role in the high-energy radiation-induced synthesis of the high-yield product C2F6, a dramatic enhancement of up to ∼ 2 × 10(4) in product yield per electron at 500 eV relative to that at 4 eV for some products suggests, however, that DEA is not the dominant mechanism for the high-energy radiation-induced synthesis of those products.

The role of electron scattering in electron-induced surface chemistry

“…There is very little data on Y (E) at these energies with respect to the maximum Y (E) (which is generally between 80 and 200 eV). Based on the available data for CF 3 I, 39 Fe(CO) 5 40 and methyl lactate 41 it is concluded that Y (1 eV, 2 eV) o Y (80-200 eV) . Therefore, a value of Y (E) of 0.5 times the maximum gives a reasonable upper limit for the matrix inversion and enables us to estimate the importance of the SE yield at low PE energies.…”