Statistical and non-statistical reactions in energy selected fluoromethane ions Original Research Article

The unimolecular reactions of the fluoromethane ion have been investigated by the threshold photoelectron photoion coincidence technique (TPEPICO). The breakdown curves have been measured in the energy range between the adiabatic ionization potential of 12.53 eV and 21 eV. In this energy range the formation of the CH2F+, CHF+, CH2+, CH3+, and CF+ fragment ions is observed. The appearance energies (AE) for these ions at 300 K are 13.2, 13.91, 13.93, 14.51 and < 17.7 eV respectively. The 0 K threshold energy for the formation of CH2F+ ions is 13.37 eV. Two different pathways for the unimolecular reaction of the fluoromethane ion can be distinguished. The reaction proceeding through the electronic ground state of the ion is entirely statistical. In contrast to this the reaction occurring through the first electronic excited state shows non-statistical behaviour. The two pathways are distinguished via the kinetic energy released in the respective dissociation channels. While all thermochemically allowed reaction channels are observed on the ion ground state potential, the first excited state seems to decay predominantly by F loss reaction.