MASS-SPECTROMETRY STUDIES OF THE IONIZATION OF ORGANIC-MOLECULES BY LOW-ENERGY POSITRONS

Positrons having energies in the range of 0.2-10 eV have been used to ionize large organic molecules. For positrons having energies above 2-3 eV ionization Occurs by positronium formation. In this paper new results are reported that describe the ionization of molecules at energies below the positronium formation threshold. Contrary to expectations, ionization by positrons having energy below the positronium threshold has been found to induce extensive fragmentation in sigma-bonded molecules. The necessary energy for ionizing the molecules and inducing fragmentation is supplied through the positron-electron annihilation process.