### Session FTP1: Poster Session I (19:00-21:30)

7:00 PM–7:00 PM, Tuesday, October 14, 2008
Room: Salon F-J

Chair: I. Langmuir

Abstract ID: BAPS.2008.GEC.FTP1.95

### Abstract: FTP1.00095 : Role of multimode excitations and inelastic escape channels in positron-molecule attachment

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#### Authors:

C.M. Surko
(Univ. of California, San Diego)

J.A. Young
(Jet Propulsion Lab)

Experiments have shown that positrons, like electrons, can attach a variety of molecules via vibrational Feshbach resonances (VFR). Because of the positron's unique annihilation channel, one can probe particularly short-lived resonances by examining features in the positron energy-resolved annihilation spectra. We discuss here energy-resolved annihilation spectra for a variety of molecules and relate these results to theory [1]. In particular, we examine the role of multi-mode excitations, which are found to produce VFR in a number of small molecules [2] and may participate in the enhancement of single-mode resonances in large molecules [3]. Also discussed is how fluorine substitution in a large hydrocarbons produces a strong inelastic escape channel. This, in turn, limits resonance lifetimes and decreases the magnitudes of the annihilation resonances above the inelastic threshold [3]. \\ ~[1] G. F. Gribakin \& C. M. R. Lee, \textit{Phys. Rev. Lett.}, \textbf{97}, 193201 (2006). \\ ~[2] J. A. Young, C. M. Surko, G. F. Gribakin, \& C. M. R. Lee, \textit{Phys. Rev. A}, in press (2008). \\ ~[3] J. A. Young \& C. M. Surko, \textit{Phys. Rev. A}, \textbf{77}, 052704 (2008).

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2008.GEC.FTP1.95