Positron-monosilane (SiH4) collisions at low, intermediate and high energies using a spherical complex optical potential approach

The author reports the first calculations on the total (elastic plus inelastic) cross sections ( sigma t ) of positron-SiH 4 scattering in a wide energy range (1-400 eV). A spherical complex optical potential (SCOP) is generated between the target and the projectile and treated exactly in a partial-wave analysis to extract complex phaseshifts. The real part of the optical potential consists of an accurate repulsive static term calculated from one-centre near-Hartree-Fock silane wavefunctions plus a polarisation potential of the correct asymptotic form (- alpha 0 /2r 4 , where alpha 0 is the dipole polarisability of the molecule) smoothly joined with the target correlation energy at short distances. For the imaginary part of the SCOP, he employs a recently semi-empirically derived form, which is based on the electron absorption potential. The final sigma t results compare fairly well with the only available measurements of Sueoka and Mori. In particular, the present model reproduces the sharp rise of sigma t near the positronium formation threshold and a bell-shaped feature around 20 eV. Below the positronium threshold, his elastic cross sections agree to within 2-3% with the more rigorous close-coupling results of Jain et al. (1986).