Time-Dependent Coupled-Channel Calculations of the Annihilation Rate in Positron–Hydrogen Collisions

We calculate the positron annihilation rate in positron–hydrogen collisions for positron energies of 250 meV–6.5 eV using a time-dependent coupled channel method. A semiempirical model recently proposed in Phys. Rev. Lett. 79 (1997), 2241 predicts that the annihilation rate prominently enhances through virtual positronium formation as the positron energy approaches the positronium formation threshold (6.8 eV) from 4 eV. We illustrate time evolution of wave functions to show that such a prominent enhancement of the annihilation rate is not found and contribution of virtual positronium formation is not important below 6.5 eV.