DFT study of self-coupling reaction of CF2(ads) coadsorbed on Cu(111) surface for forming CF2=CF2(g)

Total energy calculations based on the density functional theory (DFT) with ultrasoft pseudopotential, generalized gradient spin-polarized approximation and the partial structural constraint path minimization (PSCPM) method were carried out to establish the energetically more favorable reaction pathways for the self-coupling reaction of coadsorbed CF2(ads) leading to the formation of CF2=CF2(ads) on the Cu(111) surface. In addition, the calculated electronic properties, namely partial density of states (PDOS), suggest that the initial breaking of the Cu(111)–CF2(ads) bond associating with the electron delocalization on the Cu(111) surface and the electron transfer from Cu(111) to both units of CF2(ads) are factors controlling the energy barrier for self-coupling reaction. Finally, the calculated energy barrier (0.310 eV) for the self-coupling reaction of CF2(ads) coadsorbed on the Cu(111) surface in comparison with that (0.204 eV) for the single α-fluoride elimination of adsorbed CF3(ads) on the Cu(111) surface qualitatively manifests that the formation of CF2 = CF2(g) at 250 K is limited by the self-coupling reaction of coadsorbed CF2(ads) instead of the single α-fluoride elimination of adsorbed CF3(ads).