Berlin 2005 – scientific programme

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MO: Molekülphysik

MO 13: He and Molecular Clusters

MO 13.6: Talk

Friday, March 4, 2005, 15:45–16:00, HU 2097

Laser desorption of nanoclusters and biomolecules — •Lucia Hackermüller, Gregor Kiesewetter, Martin Berninger, and Markus Arndt — Institut für Experimentalphysik, Universität Wien, Boltzmanng. 5, A-1090 Wien

Molecule interferometry requires sufficiently intense sources of cold, neutral and intrinsically mass selected molecular beams. Laser desorption is known to generate a large fraction of neutral particles at moderate velocities. We investigate the matrix-free desorption behaviour of ligand-stabilized Au₁₁ and ’Au₅₅’ nanoparticles as well as molecules of biological relevance such as tripeptides and porphyrins. We characterize the neutral content of the emerging plume by velocity-selective multi-photon ionization at 266 nm followed by time-of-flight mass spectrometry.

Gold nanoclusters: Gold nanocrystals exist in a quasi-monodisperse form in solution, because of their protecting ligand-shell. In the desorption process the organic shell is completely removed and a full series of pure gold clusters up to Au₂₅ appears. The observed cluster number distribution can be well represented by a double power law, with exponents in good numerical agreement with predictions for clusters near their critical point. The measured mean velocities are mass dependent and range from 500 to 600 m/s.

Biomolecules: Porphyrins and amino acids can be desorbed without major fragmentation or clustering, showing a velocity distribution centred at 300 m/s. We discuss the proposed use of laser desorption sources in Talbot-Lau interferometry and Moiré deflectometry