Molecular Spectroscopy


The isolation of single cold atoms or molecules is a desirable goal for spectroscopic investigations. Bringing individual particles (of different species) together in a controlled fashion offers fundamental new possibilities for investigations of structure and dynamics.

In recent years, superfluid helium nanodroplets (HeN) have become the most flexible tool to assemble, cool, and investigate single atoms, molecules, and clusters [Callegari2011]. They combine probably the best aspects of high-resolution spectroscopy and matrix isolation; He is the most weakly interacting solvent in existence. Virtually any species can be isolated in a HeN, where it is cooled to the droplet temperature of 0.4 K. More dopants on the same HeN are at the same time confined and free to move within the droplet, and thus interact with each other, often resulting in highly unstable atomic and molecular adducts.

Our research objective is the tailored synthesisi of molecules and nanoclusters in the beneficial environment of He droplets, accompanied by their characterization, to which two labs are devoted:

  • Cluster lab I is specialized on cw and nanosecond laser-spectroscopic investigations of doped HeN, combining a wide range of lasers and detection methods: laser-induced fluorescence, multi photon ionization, magnetic circular dichroism, surface ionization, quadrupole- and time-of-flight mass selection. In recent years have obtained a comprehensive understanding of alkali-metal doped HeN: monomers, homo- and heteronuclear dimers and trimers, clusters, atomic Rydberg states, and ions.
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  • Cluster lab II was established for magnetic studies in doped HeN. The first magnetic resonance experiment in a HeN - electron spin resonance on single alkali-metal atoms located on the droplet surface - was demonstrated in 2008.
    Additionally, relaxation mechanisms triggered by electronic excitation of metal atoms (chromium, copper) are studied.

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Selected Publications

Carlo Callegari and Wolfgang Ernst Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave RegimeHelium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime1551-1594 Publikation in PURE anzeigen

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All images © TU Graz/Institute of Experimental Physics

Group members

Prof. Wolfgang E. Ernst
+43 (316) 873-8140

Ass.Prof. Markus Koch
+43 (316) 873-8161

Dr. Florian Lackner