Electronic Spectroscopy of He@C-60(+) for Astrochemical Consideration

The electronic spectrum of the endohedral fullerene He@C-60(+) observed by messenger spectroscopy in a cryogenic ion trap is presented. The role played by the messenger tag in the adopted experimental method is evaluated by recording spectra of He@C-60(+) - He-n with n = 1-4. The results indicate a linear shift of similar to 0.7 angstrom in the wavelengths allowing accurate gas phase values to be reported. The presence of the helium inside the cage shifts the absorption bands by 2-3 angstrom toward shorter wavelengths compared to C-60(+). The magnitude of this displacement will enable searches for the spectral signatures of this fullerene analogue in interstellar environments by absorption spectroscopy. The implications for potential astronomical detection are discussed.