Small He clusters with aromatic molecules

Excitation spectra of ultracold (T=0.4 K) large aromatic molecules (naphtha lene, anthracene, and tetracene) solvated by a few (1-16) He atoms are repo rted. Measured spectral shifts and vibronic excitations for a series of mas s selected He clusters are presented. Clusters on aromatic molecules with a n increasing number of rings show unexpected, and size-dependent, spectral effects. We suggest that the novel spectroscopic features are due to the an isotropic delocalization of the He atoms on the surface of the aromatic mol ecule. (C) 2001 American Institute of Physics.