Electron-triggered processes in halogenated carboxylates: dissociation pathways in CF 3 COCl and its clusters.

Trifluoroacetyl chloride, CF 3 COCl, is produced in the Earth's atmosphere by photooxidative degradation of hydrochlorofluorocarbons, and represents a potential source of highly reactive halogen radicals. Despite considerable insight into photochemistry of CF 3 COCl, its reactivity towards electrons has not been addressed so far. We investigate the electron ionization and attachment in isolated CF 3 COCl molecules and (CF 3 COCl) N , max. N ≥ 10, clusters using a molecular beam experiment in combination with quantum chemical calculations. The ionization of the molecule at 70 eV electron energy leads to strong fragmentation: weakening of the C-C bond yields the CF 3 + and COCl + ions, while the fission of the C-Cl bond produces the major CF 3 CO + fragment ion. The cluster spectra are dominated by M n ·COCl + and M n ·CF 3 CO + ions (M = CF 3 COCl). The electron attachment at energies between 1.5 and 11 eV also leads to the dissociation of the molecule breaking either the C-Cl bond at low energies below 3 eV yielding mainly Cl - ions, or dissociating the C-C bond at higher energies above 4 eV leading mainly to CF 3 - ions. In the clusters, the intact M n - ions are stabilized after electron attachment at low energies with contribution of M n ·Cl - fragment ions. At higher energies, the M n ·Cl - fragments dominate the spectra, and C-C bond dissociation occurs as well yielding M n ·CF 3 - . Interestingly, M n ·Cl 2 - ions appear in the spectra at higher energies. We briefly discuss possible atmospheric implications.