POSITRON IONIZATION MASS-SPECTROMETRY - IONIZATION OF ORGANIC-MOLECULES BY POSITRONIUM FORMATION

Low-energy (<10 eV) positrons have been used to ionize organic molecules in the gas phase followed by mass spectrometric analysis. High-energy positrons from a linear electron accelerator-based facility are re-moderated to less than 3 eV and trapped in a miniature Penning trap where they interact with the target molecules. Ions thus formed are mass analyzed in a time-of-flight mass spectrometer. The predominant ionization mechanism in this energy regime involves positronium formation and the spectra are comparable to electron impact spectra at energies a few eV above the ionization energy of the molecules. © 1990.