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

## TL;DR

This paper studies the photoionization of C70 molecules and their cations, providing insights into their electronic and vibrational states relevant to astrophysics.

## Contribution

The study presents the first threshold photoelectron spectrum of C70 and a novel semiempirical method to derive its ionization energy.

## Key findings

- The adiabatic ionization energy of C70 is measured as 7.429 eV ± 0.015 meV.
- Vibrational assignments for C70+ are suggested using a Jahn–Teller formalism.
- Electronic states of C70+ are analyzed using high-resolution He-tagging and TPES data.

## Abstract

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.