Detection of Buckminsterfullerene emission in the diffuse interstellar medium

Emission of fullerenes in their infrared vibrational bands has been detected in space near hot stars. The proposed attribution of the diffuse interstellar bands at 9577 and 9632 Å to electronic transitions of the buckminsterfullerene cation (i.e. [Formula: see text]) was recently supported by new laboratory data, confirming the presence of this species in the diffuse interstellar medium (ISM). In this letter, we present the detection, also in the diffuse ISM, of the 17.4 and 18.9 microm emission bands commonly attributed to vibrational bands of neutral C₆₀. According to classical models that compute the charge state of large molecules in space, C₆₀ is expected to be mostly neutral in the diffuse ISM. This is in agreement with the abundances of diffuse C₆₀ we derive here from observations. We also find that C₆₀ is less abundant in the diffuse ISM than in star-forming regions, supporting the theory that C₆₀ can be formed in these regions.