Fullerenes, and in particular the most stable small fullerene C₆₀, were sought for quite extensively. Initially, they appeared to be rather elusive. Shortly after the definitive detection of C₆₀ and C₇₀, described below in the C₇₀ subsection, they appeared to be almost ubiquitous as described below and in the Extragalactic section. However, a very recent laboratory spectroscopic investigation by
W. W. Duley and A. Hu,
Fullerenes and Proto-fullerenes in Interstellar Carbon Dust,
Astrophys. J. 659, Art. No. L11 (2012);
concluded that the presence of PAH molecules and of fullerenes are mutually exclusive. In fact, the dehydrogenation of PAHs involves pseudo-fullerenes which still contain H atoms and which are not as symmetric as C₆₀. Prior to turning to fullerenes, these molecules exhibit IR bands similar to C₆₀, but in addition a strong mode near 16.4 μm (610 cm^–1). The IR bands of fullerenes are apparently less specific than had been thought. This fact, however, had been known for the mid-infrared features of PAHs for a long time. As a consequence, the authors cast doubt on all reported detections of C₆₀ described in this section and in the Extragalactic section. The only uncontested report appears to be the one in which C₆₀ and C₇₀ were detected in Tc 1, see below.

Probably the first, tentative report, which seemed to be substantiated later, was published by
M. W. Werner, K. I. Uchida, K. Sellgren, M. Marengo, K. D. Gordon, P. W. Morris, J. R. Houck, and J. A. Stansberry,
New Infrared Emission Features and Spectral Variations in NGC 7023,
Astrophys. J. Suppl. Ser. 154, 309–314 (2004).
The reflection nebula was studied with Spitzer. In a note added in proof, they mentioned that M. Jura of UCLA pointed out that features at 17.4 and about 19.0 μm may be assigned to C₆₀.
A more recent and more detailed account by
K. Sellgren, K. I. Uchida, and M. W. Werner,
The 15–20 μm //Spitzer// Spectra of Interstellar Emission Features in NGC 7023,
Astrophys. J. 659, 1338–1351 (2007)
concluded that if the two modes are due to C₆₀, then the 17.4 μm band is overlapped in certain spatial regions.
An even more recent paper by
K. Sellgren, M. W. Werner, J. G. Ingalls, J. D. T. Smith, T. M. Carleton, and C. Joblin,
C₆₀ in Reflection Nebulae,
Astrophys. J. 722, L54–L57 (2010)
emphasizes that C₆₀ should be present not only in NGC 7023, but also NGC 2023 because in addition to the two bands described above, a third of four fundamental vibrations seem to have been observed near 7.0 μm. The remaining band at 8.5 μm is strongly overlapped. The authors estimate that between 0.1 and 0.6 % of the interstellar carbon is locked up in C₆₀.

Shortly before, however, a different article reported on the firm identification of C₆₀ and C₇₀ as described in the C₇₀ section.

Three out of the four fundamental modes of C₆₀ have reportedly been identified toward a star in the transition state from AGB star to planetary nebula by
Y. Zhang and S. Kwok,
Detection of C₆₀ in the Protoplanetary Nebula IRAS 01005+7910,
Astrophys. J. 730, Art. No. 126 (2011).

C₆₀ was suggested to be present in R Coronae Borealis (RCB) stars, which are very hydrogen-poor, but rich in He and C. In fact, it was found only in DY Cen and possibly V854 Cen, two comparatively H-rich RCB stars, by
D. A. García-Hernández, N. Kameswara Rao, D. L.Lambert,
Are C₆₀ Molecules Detectable in Circumstellar Shells of R Coronae Borealis Stars?,
Astrophys. J. 729, Art. No. 126 (2011).

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J. Cami, J. Bernard-Salas, E. Peeters, and S. E. Malek,
reported on
Detection of C₆₀ and C₇₀ in a Young Planetary Nebula,
Science 659, 1180–1182 (2010).
They have used archival Spitzer data of Tc 1. The C₆₀ features at 17.4 and 18.9 μm overlap with slightly weaker C₇₀ features at similar positions. The 8.5 μm feature of C₆₀ was also observed, the one near 7.0 μm is overlapped by a much stronger Ar⁺ line. Weak C₇₀ features at 12.5, 14.8, 15.6, and 21.8 μm seem to be free from overlap.
The authors point out that both C₆₀ and C₇₀ are unlikely to be in the gas phase. Rather, they reside on grains. An excitation temperature of 330 K was derived for C₆₀ whereas 180  was obtained for C₇₀, indicating the latter to occur farther out from the star.
Up to now, this article appears to be the only uncontested report on C₆₀ and C₇₀ because features commonly assigned to PAHs are absent in Tc 1.

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Contributor(s): H. S. P. Müller; 10, 2010; 06, 2011; 01, 2012

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