Hannover 2010 – scientific programme

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MO: Fachverband Molekülphysik

MO 9: Poster: Collisions, Energy Transfer

MO 9.5: Poster

Tuesday, March 9, 2010, 16:00–18:30, Lichthof

Three-dimensional velocity map imaging: Setup and resolution improvement compared to three-dimensional ion imaging — S. Kauczok¹, N. Gödecke¹, A. Chichinin^1,2, •M. Veckenstedt¹, C. Maul¹, and K.-H. Gericke¹ — ¹Institut für Physikalische und Theoretische Chemie, TU Braunschweig — ²Institute of Chemical Kinetics and Combustion, Novosibirsk, Russia

For many years 3D ion imaging has not benefitted from the introduction of ion optics into chemical imaging. Thus, a lower resolution of kinetic energy as in comparable techniques making use of inhomogeneous electric fields was inevitable. This was basically due to the fact that a homogeneous electric field was needed in order to obtain the velocity component in the direction of the time of flight spectrometer axis. In our approach we superimpose an Einzel lens field with the homogeneous field. We use a simulation based technique to account for the distortion of the ion cloud caused by the inhomogeneous field.

In order to demonstrate the gain in kinetic energy resolution compared to conventional 3D Ion Imaging, we use the spatial distribution of H⁺ ions emerging from the photodissociation of HCl following the two photon excitation to the V¹Σ⁺ state. So far a figure of merit of approximately four has been achieved, which means in absolute numbers Δv/v=0.022 compared to 0.086 at v=17000 m/s.

HBr photodissociation at 243 nm was used to recognize and eliminate systematic deviations between simulation and experimentally observed distribution. The technique has also proven to be essential for the precise measurement of translationally cold distributions.