$C_{60}^{+}$ in diffuse clouds: laboratory and astronomical comparison

The wavelengths of the strongest absorptions in the electronic spectrum of $C_{60}^{+}$ have been determined by experimental investigation into the perturbation caused by the helium in the laboratory spectra of $C_{60}^{+}-{He}_n(n=1\text{--}3)$. The extrapolation of these gives absorption bands of bare $C_{60}^{+}$ at 9348.4, 9365.2, 9427.8, 9577.0, and 9632.1 Å, with ±0.2 Å as the 2σ uncertainty. The laboratory data are compared with the complete set of astronomical observations reported in the literature. The spectral characteristics are found to be in agreement with five diffuse interstellar bands, for which the systematic uncertainties are larger than for the laboratory data.