On the dissociation dynamics of energy-selected dimethylether ions

Dissociation of the dimethylether ion has been studied using threshold photoelectron-photoion coincidence (TPEPICO) mass spectrometry. Our TPEPICO breakdown curves showed a significant occurrence of electronic autoionization at around 12.2 eV and over 16 eV. For the formation of [CH3O]+, rectangular flight-time distributions owing to a large, sharp kinetic energy release were observed at high energies, and about 80% of internal excess energy of the molecular ion was found to be released as translational energy in this fragmentation. This remarkably high conversion was consistent with the spectator model of direct dissociation rather than with statistical theories (RRKM—QET). However, the relative abundance of [CH3O+] remained less than 20% in the breakdown diagram although direct dissociation predicts its predoiminace. These results may be intepreted as a direct dissociation to CH3O+ on a repulsive state reached by transition from an initial state or as a statistical fragmentation to CH2O+ H strongly controlled by a tight transition exit on a high reverse activation barrier.