Experimental VUV Photoionization of C70 and Vibrationally Resolved Spectra of the Excited Electronic States of the C70 + Cation.

The nature of the photoionization of fullerenes is of significant interest to molecular astrophysics and astrochemistry. The C60 + cation has been identified as a carrier of five of the diffuse interstellar bands (DIBs), and recent correlations between C70 + electronic bands and a few weak DIBs have been presented. In this work, we present a high-resolution electronic spectrum of C70 + recorded with He-tagging messenger spectroscopy, as well as the first threshold photoelectron spectrum (TPES) of C70. We comment on the He cage stability around C70 + and how it differs from that around other fullerenes, and we suggest some tentative vibrational assignments to the electronic spectrum based on a Jahn-Teller type formalism, which is expected from the C70 + system. We use a novel semiempirical method employing the high-resolution He-tagging spectrum and create band fits that we compare with the TPES to derive the adiabatic ionization energy of C70 (7.429 eV ± 0.015 meV). This methodology comes with some significant limitations but allows us to tentatively derive the energies of other excited states of the C70 + cation from the TPES.