Hannover 2013 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 24: Atomic clusters II (with A)

MO 24.1: Hauptvortrag

Donnerstag, 21. März 2013, 14:00–14:30, F 428

Size selective vibrational spectroscopy of strongly bound neutral clusters — •Andre Fielicke — Institut für Optik und atomare Physik, TU Berlin

Properties of small clusters are often not only strongly dependent on their size but also on their charge state. A prominent example for this is the transition from 2D to 3D structures for gold clusters which is observed to occur at n=8 for the cations and at n=12 for the anions. While such ionic clusters are susceptible to common mass spectrometric techniques for size selection and storage similar manipulations are more difficult for neutral species and, hence, different experimental techniques need to be applied to obtain cluster size specific information. Recently, different methods have been developed that apply resonant vibrational excitation of strongly bound neutral clusters in molecular beams with infrared Free Electron Lasers. These IR sources provide intense and tunable radiation even in the far-IR region where the vibrational fundamentals of metal or semi-metal clusters are located. Size selectivity is obtained by coupling the IR excitation with a subsequent soft ionization step, i.e. avoiding fragmentation, and mass spectrometric analysis of the ionic distribution. Examples of such action spectroscopic IR studies on neutral clusters are the dissociation of messenger complexes of metal clusters,[1] IR-UV two color ionization of semi-metal and oxide clusters [2] and IR resonant enhanced multiple photon ionization of clusters of refractory materials. [1] P. Gruene et al., Science 321, 674 (2008); [2] M. Haertelt et al., Phys. Chem. Chem. Phys. 14, 2849 (2012).