Ionization-site effects on the photofragmentation of chloro- and bromoacetic acid molecules

Abstract

<p> Fragmentation of gas-phase chloro- and bromoacetic acid samples, particularly its dependency on the atomic<br /> site of the initial core ionization, was studied in photoelectron-photoion-photoion coincidence (PEPIPICO)<br /> measurements. The fragmentation was investigated after ionizing carbon 1s and bromine 3d or chlorine 2p<br /> core orbitals. It was observed that the samples had many similar fragmentation pathways and that their relative<br /> weights depended strongly on the initial ionization site. Additional Auger PEPIPICO measurements revealed a<br /> clear dependence of fragment pair intensities on the kinetic energy of the emitted Auger electrons. The modeled<br /> and measured Auger electron spectra indicated that the average internal energy of the molecule was larger<br /> following the carbon 1s core-hole decay than after the decay of the halogen core hole. This difference in the<br /> internal energies was found to be the source of the site-dependent photofragmentation behavior.</p>