Computing positron annihilation in polyatomic gases: An exploratory study

The rates of positron annihilation in molecular gases are known to depend on the nanoscopic structural features of the ambient molecules. The aim of the present study is to explore the possible relationships that exist between some of the most salient molecular structural features and the ensuing positron annihilation rates at room temperature. Quantum dynamical calculations are applied to a broad variety of polyatomic targets using a parameter-free model interaction with the impinging positrons. The Zeff values, as well as the integral elastic cross sections, are computed for such systems over the relevant range of collision energies. The dynamical treatment is shown to yield realistic values for the cross sections and to produce Zeff values whose agreement with the few existing measured data varies greatly from one system to another.