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Abstract

The triatomic H+3 molecular ion plays an important role in molecular quantum dynamics through its equilateral triangular structure. Many studies of molecular reactions involving H+3 have been done thus far, among them dissociative recombination in storage ring experiments with a cold electron-beam. For these strongly energy dependent reactions, the population in individual rovibrational levels is of large importance. To determine such populations for H+ 3 ions inside a storage ring, an extremely sensitive state-selective method must be used, such as the Resonant-Enhanced Multi-Photon Dissociation (REMPD). In REMPD, molecules are highly excited from a low lying initial level in a rst resonant step and photodissociated from these high lying states in a second step. To fully employ this method, detailed investigations are necessary. Here, an experiment is presented which determines the energy range of the highly excited vibrational states of H+3 suitable for photodissociation. Additional photodissociation experiments, using hot H+3 ions in the storage ring TSR at the Max-Planck Institute for Nuclear Physics, yield an e ective lifetime of these dissociated H+3 states. Finally selective vibrational excitation of cold H+3 (the fi rst step of REMPD) is discussed with the aim of reaching the highly excited vibrational states suitable for photodissociation.