Internal energy deposition into molecules upon positron-electron annihilation

The dissociative ionization of organic molecules, induced by positrons having energies below the positronium threshold (0.5--3 eV), has been studied. Cross sections for the ionization-fragmentation processes increase as positron energies decrease. The data reveal that the energy required for dissociative ionization is supplied by the annihilation process, and that fragmentation occurs by breakage of C-C single bonds in preference to double and triple bonds.