Fragmentation of gas-phase chloro- and bromoacetic acid samples, particularly its dependency on the atomic

site of the initial core ionization, was studied in photoelectron-photoion-photoion coincidence (PEPIPICO)

measurements. The fragmentation was investigated after ionizing carbon 1s and bromine 3d or chlorine 2p

core orbitals. It was observed that the samples had many similar fragmentation pathways and that their relative

weights depended strongly on the initial ionization site. Additional Auger PEPIPICO measurements revealed a

clear dependence of fragment pair intensities on the kinetic energy of the emitted Auger electrons. The modeled

and measured Auger electron spectra indicated that the average internal energy of the molecule was larger

following the carbon 1s core-hole decay than after the decay of the halogen core hole. This difference in the

internal energies was found to be the source of the site-dependent photofragmentation behavior.