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 res ults are reported that describe the ionization of molecules at energie s 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 mole cules. The necessary energy for ionizing the molecules and inducing fr agmentation is supplied through the positron-electron annihilation pro cess.