Inhomogeneous broadening of the zero phonon line of phthalocyanine in superfluid helium droplets

The electronic origin band of the S-1<--S-0 transition of monomer phthalocy anine doped into liquid helium droplets consist of a single zero phonon lin e (ZPL) and a structured phonon wing. The latter reflects the low frequency modes of the helium droplet. At very high resolution (1 MHz) the asymmetri c spectrum of the ZPL of phthalocyanine provides no indication of a rotatio nal substructure. Changes in the asymmetry and the peak position of the ZPL with variation of the average droplet size are in very good agreement with an inhomogeneous model line shape. (C) 2001 American Institute of Physics.