Elastic Scattering of Positrons by Hydrogen Molecules

Elastic positron–hydrogen molecule collisions are considered below the first electronic excitation threshold. The interaction of the incoming positron with the hydrogen molecule is represented by a superposition of single center static and nonspherical polarization potentials. The static potential is expanded to second degree in Legendre polynomials. The Chebyshev polynomials are used to improve the truncated Legendre series approximation and the effect of including the fourth degree contribution is shown to be slight. Positronium formation effects are neglected. Two semiphenomenological polarization potentials are used, and it is shown that the parameters can be suitably adjusted to reproduce the results obtained if the Henry and Lane polarization potential is used. It is shown that the partial Ramsauer–Townsend effect is useful in determining the values of polarization potential parameters. Total elastic scattering cross sections are given for incoming positron energies between about 0.4 and 14 eV while the positron annihilation coefficient is given to about 60 eV.