Small He clusters with aromatic molecules

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