Perspective: C₆₀⁺ and laboratory spectroscopy related to diffuse interstellar bands

Area of Science:

• Laboratory astrophysics
• Astrochemistry
• Spectroscopy

Background:

• Decades of research focused on laboratory electronic spectra of organic radicals and ions.
• Species selection prioritized astrophysical relevance, especially for diffuse interstellar absorption bands.
• Studies included carbon chains and nitrogen/hydrogen-containing organic molecules.

Purpose of the Study:

• To measure laboratory electronic spectra of potential interstellar molecules.
• To enable direct comparison between laboratory and astronomical data.
• To identify the molecular carriers of diffuse interstellar absorption bands.

Main Methods:

• Development of techniques for low-temperature (interstellar medium relevant) spectral measurements.
• Gas-phase laboratory spectral measurements.
• Radiofrequency ion trap experiments at 6K.

Main Results:

• Electronic spectra of numerous organic radicals and ions were recorded.
• Many species exhibited electronic transitions in the visible spectrum, where diffuse interstellar bands are observed.
• No previously studied species matched prominent interstellar absorption features.
• The buckminsterfullerene ion (C60+) was identified as the first carrier molecule in 2015.

Conclusions:

• Laboratory spectral data are crucial for identifying interstellar molecules.
• The identification of C60+ marked a significant breakthrough in understanding diffuse interstellar bands.
• Further laboratory studies are needed to identify other interstellar absorption band carriers.