Absorption spectroscopy of C₆₀ molecules isolated in helium droplets

We have recorded the electronic absorption of cold C₆₀ molecules embedded in helium droplets at a temperature of approximately 0.4 K, using a beam depletion technique. We obtain highly resolved spectra in the region between 595 and 650 nm and are able to observe in detail the origin of the electronic transitions near 638 nm. In contrast to traditional matrix experiments the spectra show negligible shifts and little broadening. This remarkable feature could establish the technique as an alternative for gas-phase spectroscopy.