Abstract: The photoionization and dissociative photoionization of o-, p-, m-bromotoluene were investigated by utilizing synchrotron-based threshold photoelectron photoion coincidence spectroscopy (TPEPICO). Threshold photoelectron spectra (TPES), TPEPICO mass spectra and mass-selected TPEPICO spectra corresponding to each species were measured in the 8.5~12.5 eV energy range. The fundamental data including the ionization energy of bromotoluene molecules and the appearance energy of the C7H7+ fragment ions are acquired and agree well with previous literature results. Then based on the obtained average kinetic energy released in the dissociation and the existing potential energy surfaces, the dissociation mechanisms of o-, p-, m-bromotoluene ions are proposed. The bromotoluene ions with small internal energy will dissociate to benzyl ions and Br atoms after performance of inter-conversion to isomers, whereas those with large internal energy will directly fragment to the tolyl ions via the C-Br bond breaking.

Key words: bromotoluene, dissociation dynamics, photoelectron photoion coincidence, ionization energy, threshold photoelectron spectrum