Site-selective photochemistry of core excited molecules: Role of the internal energy

A further insight into the photochemistry of a core excited polyatomic molecule has been obtained using a new electron-ion coincidence setup. Selecting the kinetic energy of Auger electrons in coincidence with fragment ions we observed a strong site selective fragmentation for the lowest states of the ClCH2Br2+ ion, following selective Br 3d or Cl 2p core photoionization. At higher energy the selectivity diminishes and is completely lost for the highest states. The pure photoselective effect has been emphasized by subtracting the thermodynamical, naturally selective, fragmentation pattern. [S0031-9007(98)07582-6].