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 ∼0.7 Å 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 Å 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.