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Merged Beams Experiments for Mutual Neutralization Studies.
  Molecular Physics seminar

Thursday 02 June 2016
from 10:00 to 11:00
at A4:1003
Speaker : Nathalie de Ruette (Atomic Physics Division)
Abstract : Mutual Neutralization (MN) of anions and cations is a key reaction for the ionization balance in interstellar media [1]: A+ + B− → A + B. (1) But so far, MN experimental studies have mainly been limited to collision energies down to a few eV and could not resolve the electronic (n), angular momentum (L), and spin (S) states, i.e. the LS-terms, of the neutral products [2,3]. We recently upgraded the merged beam setup in Louvain-la-Neuve to reach 5 meV collision energies, and incorporated three-dimensional momentum imaging using two position sensitive detectors. Besides providing clear coincidence signals between A and B, this technique gives unambiguous identification of LS-terms of the products via the measurement of the Kinetic Energy Release (KER). We present absolute MN cross sections for N+ colliding with O− in the 0.005-10 eV energy range and KER-spectra at subthermal energies for C + on P− , C− , Si− , O− or S− , with identifications of the capture states of the products. While several of the A + + B − systems that we have studied give results well accounted for by means of simple multi-channel Landau-Zener calculations, there are striking exceptions for the C+ + O− and C+ + P− systems. The present study will also serve to benchmark merged ion beams studies at the double electrostatic storage ring DESIREE now in operation at Stockholm University [4,5]. With DESIREE it will be possible to study MN between molecular ions with very low internal temperatures (down to 10 K). [1] M. Larsson, W. D. Geppert, and G. Nyman, Rep. Prog. Phys. 75, 066901 (2012). [2] M. Terao, S. Szücs, M. Cherkani, F. Brouillard, R. J. Allan, C. Harel, and A. Salin, Europhys. Lett. 1, 123 (1986). [3] S. M. Nkambule, N. Elander, ˚ A. Larson, J. Lecointre, and X. Urbain, Phys. Rev. A 93, 032701 (2016). [4] R. D. Thomas, et al., Rev. Sci. Instrum. 82, 065112 (2011). [5] H. T. Schmidt, et al., Rev. Sci. Instrum. 84, 055115 (2013).

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