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Photoabsorption of Ag Clusters in He Droplets: A Transition from Single- to Multi-Centered Growth 67 th International Symposium on Molecular Spectroscopy.

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Presentation on theme: "Photoabsorption of Ag Clusters in He Droplets: A Transition from Single- to Multi-Centered Growth 67 th International Symposium on Molecular Spectroscopy."— Presentation transcript:

1 Photoabsorption of Ag Clusters in He Droplets: A Transition from Single- to Multi-Centered Growth 67 th International Symposium on Molecular Spectroscopy Luis F. Gomez 1, Evgeny Loginov 1, Naihao Chiang 2, Avik Halder 2, Nicholas Guggemos 2, Vitaly V. Kresin 2, and Andrey F. Vilesov 1,2 1 Department of Chemistry, University of Southern California, Los Angeles, USA 2 Department of Physics and Astronomy, University of Southern California, Los Angeles, USA

2 2 N He ~ 10 4 Small Droplets vs. Larger Droplets

3 Pulsed laser 3 Measuring the Spectra of Ag Clusters in Helium

4 Henne & Toennies, JCP (1998). Lewerenz et al, CPL (1993). Titration with Helium 4 He Droplet Sizes Gomez, Loginov, Sliter, Vilesov, J. Chem. Phys. (2011)

5 P He E He = 0.06 meV He-He N binding energy E Ag = 3 eV Ag binding energy = avg. number of He atoms in droplet Calorimetry in He Droplets 5 ∆P ~ He flux

6 Ag[…4d 10 5s 1 ] Loginov, Gomez, Chiang, Halder, Guggemos, Kresin, Vilesov, PRL (2011) 6 Spectra of Small Ag Clusters in Droplets + + + - - - + + + - - - + + + - - - + + + - - - + + + -- - + + + - - - + + + - - - + + + - - - + + + - - - + + + - - - + + + - - - + + + - - - + + + - - - + + + - - - + + + - - - + + + - - -

7 Loginov, Gomez, Chiang, Halder, Guggemos, Kresin, Vilesov, PRL (2011) 7 Unexpected Strong IR Absorption in Large Ag Clusters

8 + + + - - - + + + - - - + + + - - - + + + - - - ≈ 0.5 eV + + + - - - + + + - - - + + + - - - + + + - - - 8 Origin of the Broadening in the Spectra of Metal Cluster-Cluster Aggregates: Dipole-Dipole Interaction of Excited Clusters

9 Recombination time of two Ag atoms Time between pickup events 9 Kinetics of Ag Cluster Growth in a Droplet

10 10 Loginov, Gomez, Chiang, Halder, Guggemos, Kresin, Vilesov, PRL (2011) Different Modes of Cluster Formation in the Droplets

11 Large superfluid He droplets can be used for metal cluster growth Small Ag clusters less than ~100 atoms are compact Larger Ag clusters are likely aggregates Found average sizes of very large droplets: ~ 10 8 – 10 10, up to 1 µm in diameter Conclusions


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