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Title: Dynamics of gas phase Ne{sup *} + NH{sub 3} and Ne{sup *} + ND{sub 3} Penning ionisation at low temperatures

Two isotopic chemical reactions, Ne{sup *} + NH{sub 3}, and Ne{sup *} + ND{sub 3}, have been studied at low collision energies by means of a merged beams technique. Partial cross sections have been recorded for the two reactive channels, namely, Ne{sup *} + NH{sub 3} → Ne + NH{sub 3}{sup +} + e{sup −}, and Ne{sup *} + NH{sub 3} → Ne + NH{sub 2}{sup +}+ H + e{sup −}, by detecting the NH{sub 3}{sup +} and NH{sub 2}{sup +} product ions, respectively. The cross sections for both reactions were found to increase with decreasing collision energy, E{sub coll}, in the range 8 μeV < E{sub coll} < 20 meV. The measured rate constant exhibits a curvature in a log(k)-log(E{sub coll}) plot from which it is concluded that the Langevin capture model does not properly describe the Ne{sup *} + NH{sub 3} reaction in the entire range of collision energies covered here. Calculations based on multichannel quantum defect theory were performed to reproduce and interpret the experimental results. Good agreement was obtained by including long range van der Waals interactions combined with a 6-12 Lennard-Jones potential. The branching ratio between the two reactive channels, Γ=([NH{sub 2}{sup +}])/([NH{sub 2}{sup +}]+[NH{submore » 3}{sup +}]) , is relatively constant, Γ ≈ 0.3, in the entire collision energy range studied here. Possible reasons for this observation are discussed and rationalized in terms of relative time scales of the reactant approach and the molecular rotation. Isotopic differences between the Ne{sup *} + NH{sub 3} and Ne{sup *} + ND{sub 3} reactions are small, as suggested by nearly equal branching ratios and cross sections for the two reactions.« less
Authors:
; ;  [1] ;  [2] ;  [3]
  1. Institute for Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne (Switzerland)
  2. Faculty of Physics, University of Warsaw, Hoża 69, 00-681 Warsaw (Poland)
  3. Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw (Poland)
Publication Date:
OSTI Identifier:
22311286
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 140; Journal Issue: 24; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AMMONIA; BRANCHING RATIO; CHEMICAL REACTIONS; COLLISIONS; CROSS SECTIONS; DEUTERIDES; INTERACTIONS; IONIZATION; IONS; LENNARD-JONES POTENTIAL; MEV RANGE; QUANTUM MECHANICS; REACTION KINETICS; ROTATION; VAN DER WAALS FORCES