Positronium formation and ionization in slow positron-hydrogen atom collisions

The electron capture and ionization processes in slow collisions of positro ns with hydrogen atoms are considered within the advanced adiabatic approac h to atomic collisions. The mass asymmetry of the (p, e(-), e(+)) collision system is properly taken into account. The calculated positronium formatio n and ionization cross sections compare favourably with the available exper imental data in the adiabatic energy region. It is shown that the potential energy curve of the 2p sigma molecular state supports a quasi-bound level of the three-particle (p, e(+), e(-)) system with an energy of -0.3 eV and decay width of 0.15 eV, approximately.