Gamma-ray spectra from low-energy positron annihilation processes in molecules

Abstract

The theoretical $\ensuremath{\gamma}$-ray spectra from positron-electron annihilation process in a wide variety of atoms and molecules are studied. The theoretical Doppler broadened $\ensuremath{\gamma}$-ray spectra for core, inner valence, and outer valence electrons of these molecules are studied systematically. The present results show that the experimental $\ensuremath{\gamma}$-ray spectra agree well with inner valence electrons, especially the lowest occupied valence orbital electrons rather than the outer valence electrons. These inner valence electrons show a strong correlation with the corresponding available experimental measurements. These findings are interesting because the outer valence electrons have been supposed to have larger probability annihilating with positrons rather than the inner valence electrons. The present work also suggests that the accurate positron wave functions must be involved to identify the dominance of the bound electrons clearly in positron-electron annihilation process.