Improving the wavefunction of the Schwinger multichannel method for positron scattering-II: Application for elastic and inelastic e+ - H2 scattering

In the present paper, we propose a development to the Schwinger multichannel (SMC) method (Germano J S E and Lima M A P 1993 Phys. Rev. 47 3976) for the elastic and inelastic scattering of positrons by targets of arbitrary geometry. The essence of this work is based on the fact that the main limitation of the SMC method for positron scattering lies in what makes it a general method, i.e. the expansion of the scattering function is done in an L-2 basis (Cartesian Gaussian functions) and this is very effective for short-range potentials. Our effort is to improve the SMC method through the use of plane waves as trial functions (SMC-PW) (Lino J L S 2007 Phys. Scr. 76 521). In order to do this, we have to evaluate reliable codes involving matrix elements of the type <(k) over right arrow (f) | VG(o)((+))V |(k) over right arrow (i)>, which is done here by direct numerical quadrature. Calculated elastic differential and inelastic integral cross sections for positron-H-2 collisions are reported. For the elastic scattering, we discuss a mechanism for the Buckingham polarization model using an adjustable energy-dependent parameter at intermediate energies in the range 50-200 eV. We also present a preliminary study on the excitation of the X-1 Sigma(+)(g) -> B-1 Sigma(+)(u) transitions in H-2. Our calculations for inelastic scattering cover the impact range of 13.5-30 eV investigated by Arretche and Lima (2006 Phys. Rev. A 74 042713) using the traditional SMC method. Our inelastic and elastic cross sections are found to be in reasonable agreement with other theoretical studies and experimental data.