Annihilation rates of low-energy positron scattering from simple diatomic molecules

We discuss the calculations of Zeff coefficients for a series of diatomic molecules over the range of energies below the positronium formation. During the development of a general code for polyatomic, nonlinear molecules colliding with positrons, it was discovered that the earlier one, employed only for diatomic molecules, had an error. The error is corrected and the corrected results are presented here. We also discuss a way of including a density-dependent enhancement factor when calculating Zeff values which is known to improve agreement with experiments in solids and we find that it also brings our calculations closer the available data for gaseous systems.