C$_{60}^+$ and the Diffuse Interstellar Bands: An Independent Laboratory Check

TL;DR

This study refines the laboratory wavelengths of C60+ ion absorption features, crucial for understanding diffuse interstellar bands, using high-resolution laser spectroscopy of ultracold helium droplet-embedded ions.

Contribution

It introduces a new high-resolution laser dissociation spectroscopy method to accurately determine C60+ wavelengths, improving upon previous techniques that used wavelength-dependent photodissociation.

Findings

Precise rest wavelengths for C60+ bands are established.

Band widths and intensity ratios are analyzed.

Results support the identification of C60+ as the carrier of certain DIBs.

Abstract

In 2015, Campbell et al. (Nature 523, 322) presented spectroscopic laboratory gas phase data for the fullerene cation, C$_{60}^+$, that coincide with reported astronomical spectra of two diffuse interstellar band (DIB) features at 9633 and 9578 \AA. In the following year additional laboratory spectra were linked to three other and weaker DIBs at 9428, 9366, and 9349 \AA. The laboratory data were obtained using wavelength-dependent photodissociation spectroscopy of small (up to three) He-tagged C$_{60}^+-$He$_n$ ion complexes, yielding rest wavelengths for the bare C$_{60}^+$ cation by correcting for the He-induced wavelength shifts. Here we present an alternative approach to derive the rest wavelengths of the four most prominent C$_{60}^+$ absorption features, using high resolution laser dissociation spectroscopy of C$_{60}^+$ embedded in ultracold He droplets. Accurate wavelengths of the bare fullerene cation are derived based on linear wavelength shifts recorded for He$_n$C$_{60}^+$ species with $n$ up to 32. A careful analysis of all available data results in precise rest wavelengths (in air) for the four most prominent C$_{60}^+$ bands: 9631.9(1) \AA, 9576.7(1) \AA, 9427.5(1) \AA, and 9364.9(1) \AA. The corresponding band widths have been derived and the relative band intensity ratios are discussed.