2025ApJ...992..175D

In recent years, astronomical observations, in combination with laboratory spectra and theoretical modeling, have confirmed the presence of C₆₀, ${{\rm{C}}}_{60}^{+}$ and C₇₀ across a broad range of astrophysical objects. Despite expectations that ${{\rm{C}}}_{70}^{+}$ should also be present in space, its detection is difficult to confirm due to both the lack of laboratory gas-phase IR spectra and challenges in calculating its vibrational spectrum. This study presents gas-phase IR spectroscopy of ${{\rm{C}}}_{70}^{+}$ between 6 and 9 μm (1100-1625 cm^–1) under astrochemically relevant conditions. The large discrepancies between the experimental and theoretical spectra of ${{\rm{C}}}_{70}^{+}$ highlight the challenges of calculating the complex vibrational spectrum of this ion and emphasize the need for laboratory data for comparison to astronomical observations. Additionally, new spectroscopic data of ${{\rm{C}}}_{60}^{+}$ are provided, showing the mid-IR spectra of both fullerene cations are dominated by features around 7 μm, where strong emission from planetary nebulae is observed. These results are compared with emission from SMP LMC 56 and Tc 1, providing a foundation to search for ${{\rm{C}}}_{70}^{+}$ in space.