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Superfluid helium nanodroplets provide an ideal ``refrigerator'' for high precision spectroscopy of embedded species. Recent experiments study vibrational dynamics of dimers attached to helium nanodroplets, employing femtosecond pump-probe spectroscopy [1]. Unexpected features in the spectra exhibit the influence of the helium environment on the dimer dynamics. We propose that the most important effect is a general damping of vibrational wave packets. Numerical calculations allow us to reproduce and explain crucial experimental findings, unseen in gas-phase experiments. Remarkably, best agreement with experiment is found if one allows for undamped motion of slowly moving wave packets, which might be attributed to the superfluid properties of the host. [1] P. Claas, G. Droppelmann, C. P. Schulz, M. Mudrich, and F. Stienkemeier, J. Phys. B: At. Mol. Opt. Phys. 39, 1151 (2006). |
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