Positron Annihilation in Condensed Ammonia

Abstract

Two‐photon angular correlation and lifetime studies have been performed for positron–electron pairs annihilating in liquid (− 65°C) and solid (− 105°C) ammonia. The angular distributions were the same for both the liquid and solid samples. A low‐momentum component indicated an amount of positronium formation that is consistent with the lifetime results. The momentum distribution determined from the data is compared with a calculated distribution based on a cell model, using SCF molecular orbitals for ammonia and realistic positron wavefunctions. The lifetime results are discussed in the light of the free‐volume model.