Berlin 2001 – wissenschaftliches Programm

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MO: Molekülphysik

MO 11: Theory: Structure and Dynamics

MO 11.2: Vortrag

Donnerstag, 5. April 2001, 16:00–16:15, H107

Possible Mechanisms for Low Energy Positron Annihilation in Polyatomic Molecular Gases — •Alessandro Occhigrossi, Tamio Nishimura, and Franco.A. Gianturco — Department of Chemistry, The University of Rome Citta Universitaria 00185 Rome,Italy

We shall present recent computational results for positron-molecule scattering, below the threshold of Ps formation, obtained with the Single Center Expansion method(1) for the interaction and solving the quantum dynamics of the coupled equations. Our calculations will show vibrationally elastic integral cross sections and the annihilation parameter Zeffs for C2H2, C2H4, and fluorinated methanes like CH3F and CHF3, which allows us to discuss possible microscopic mechanisms for the annihilation of low energy positrons in molecular gases. We will show that our parameter-free modelling for the interaction is capable of yielding experimental results of the total cross sections (2), while the use of the Fixed- Nuclei approximation, which decouples the positron dynamics from the molecular rovibrational states, excludes the possibility of considering resonant mechanisms as being responsible for Zeff rate-enhancement effects(3). References (1)F.A.Gianturco, T.Mukherjee, and A.Occhigrossi,submitted to J.Phys,B, (2000) (2)M.Kimura, O.Sueoka, A.Hamada, and Y.Itikawa, Adv.Chem.Phys., Vol.111(2000)537 (3)K.Iwata, G.F.Gribakin, R.G.Greaves, and C.M.Surko,Phys.Rev.A, Vol.61(2000)022719