MECHANISMS OF POSITRON ANNIHILATION ON MOLECULES
G. F. Gribakin
Two mechanisms of positron annihilation on molecules are considered: (i)
Direct annihilation similar to that for positrons on atoms; for room
temperature positrons it gives annihilation rates up to Z_eff about
1000. (ii) Resonant annihilation which proceeds via positron capture into
vibrationally excited quasibound states of the positron-molecule complex.
The latter is sensitive to the chemical composition of the molecule
and can give very high annihilation rates (Z_eff up to 10^8). Both
features agree with experimental data by the group of Surko.