Düsseldorf 2007 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 27: Poster: Collisions and Energy Transfer
MO 27.2: Poster
Dienstag, 20. März 2007, 16:30–18:30, Poster A
Crossed-beam imaging of reactive scattering — •Christoph Eichhorn, Jochen Mikosch, Sebastian Trippel, Rico Otto, Markus Debatin, Matthias Weidemüller, and Roland Wester — Physikalisches Institut, Universität Freiburg, 79104 Freiburg
Among ion-molecule reactions, the nucleophilic substitution mechanism (SN2) has gained attention because its quantum dynamics depend sensitively on the transition between entrance and exit channel complexes, which are seperated by a potential energy barrier [1]. Trajectory simulations [2] show e.g. that recrossing may lead to high internal excitation of the products.
We use crossed beam imaging in combination with sliced 3D velocity mapping, to study the differential cross section of the SN2 reaction Cl− + CH3I —→ CH3Cl + I− at relative collision energies between 0.7eV and 3eV. This allows us to measure the vibrational excitation of the CH3Cl product molecule. While at low relative energy the reaction is dominated by strong backward scattering attributed to the SN2 mechanism, much higher scattering angles are observed for higher collision energies, indicating a reaction without a collinear approach. Also an increase in the internal energy is observed.
Furthermore, we are developing the tools to study ion-molecule scattering with laser-aligned molecules [3], and laser assisted collisions.
[1] M.L.Chabinyc et al., Science, 279, 1882 (1998) [2] W.L.Hase, Science, 266, 998 (1994) [3] H.Stapelfeldt and T.Seideman, Rev. Mod. Phys. 75, 543 (2003)