Berlin 2001 – scientific programme

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A: Atomphysik

A 10: Posters Wednesday (Cooling and Trapping, Electron Scattering and Recombination)

A 10.27: Poster

Wednesday, April 4, 2001, 12:30–15:00, AT3

Positron-Impact Vibrational Excitation of Methane Molecules — •Tamio Nishimura, Alessandro Occhigrossi, and Franco A. Gianturco — Department of Chemistry, The University of Rome, Citta Universitaria 00185 Rome, Italy

Theoretical cross sections on the vibrationally inelastic scattering of positron from methane molecules are reported for the first time at collision energies less than the positronium formation threshold. They are obtained by means of an extension of the single-center expansion approach and by then solving the body-fixed vibrational close-coupling equations for the wave function of scattered positron. As for an interaction potential, effects of an ab initio electrostatic and target polarization are taken into account, and the latter quantity is approximated in the form of a parameter-free model potential. No positroniun formation channel is considered throughout the present calculation. Here vibrational excitations of the symmetric and anti- symmetric stretching modes are treated, and the sum of the inelastic cross sections for both stretching modes is compared with the experimental data which have also been provided for the two unresolved modes(1). Our results are also compared with the calculations previously

done by our group for the case of electron scattering from the methane molecule in the same range of collision energies(2). Detailed results will be presented at the conference. References (1)C.M.Surko,private communication (2)M.Cascella,R.Curik, and F.A.Gianturco,submitted to J.Phys.B(2000)