Chemical Synthesis Induced by Dissociative Electron Attachment

We have investigated reactions in condensed CF 2Cl 2induced by electrons of subexcitation energies under ultrahigh vacuum conditions. The yields of the CF 2Cl 2radiolysis products (C 2F 4Cl 2, C 2F 3Cl 3, and C 2F 2Cl 4) were determined as functions of electron energy ( Ei) (∼1 to ∼4.5 eV) and electron dose (fluence) (1.5 × 10 16e/cm 2to 2.2 × 10 16e/cm 2) by postirradiation temperature-programmed desorption. In general, we ascribe the formation of these radiolysis products to reactions of •CFCl 2and •CF 2Cl radicals, which are generated by dissociative electron attachment (DEA) to CF 2Cl 2. Consistent with condensed-phase experiments, which report the electron stimulated desorption of F −ions via transient negative ion formation at incident electron energies near 4 eV, the yield of products C 2F 2Cl 4and C 2F 3Cl 3derived from reactions of •CFCl 2show maxima near ∼3 eV. The production of C 2F 3Cl 3and C 2F 4Cl 2at electron energies as low as 2 eV indicates that •CF 2Cl is generated; however, the absence of a clear resonance maximum in the C 2F 4Cl 2yield function indicates that the production of •CF 2Cl radicals via DEA is not the sole or dominant pathway for the formation of C 2F 4Cl 2. Indeed, the variation of radiolysis product yield with electron dose suggests that the C 2F 4Cl 2signal may additionally be generated by reactions of CF 2Cl 2with the difluorocarbene radical ( :CF 2), which we propose is also formed by DEA to CF 2Cl 2. Although numerous studies have revealed chemical damage induced by DEA, our results represent one of the first studies to unambiguously demonstrate (via a clear signature of resonance) chemical synthesis induced by this process.