Show pageOld revisionsBacklinksBack to top This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong. ===== On the Thus Far Questionable Detection of Fullerenes in Extragalactic Sources ===== \\ \\ ==== C60 ==== Fullerenes, and in particular the most stable small fullerene C<sub>60</sub>, were sought for quite extensively. Initially, they appeared to be rather elusive. Shortly after the definitive Galactic detection of C<sub>60</sub> and C<sub>70</sub>, they appeared to be almost ubiquitous. However, a very recent laboratory spectroscopic investigation by\\ W. W. Duley and A. Hu,\\ **[[https://doi.org/10.1088/2041-8205/745/1/L11|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 C<sub>60</sub>. Prior to turning to fullerenes, these molecules exhibit IR bands similar to C<sub>60</sub>, but in addition a strong mode near 16.4 μm (610 cm<sup>–1</sup>). Some of 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 autors cast doubt on all reported detections of C<sub>60</sub> described in this section and in the Extragalactic section. The only uncontested report appears to be the one in which C<sub>60</sub> and C<sub>70</sub> were detected in Tc 1, see in the Galactic section. However, some of the other detection are probably likely correct, even if some caution is advised. D. A. García-Hernández, A. Manchado, P. García-Lario, L. Stanghellini, E. Villaver, R. A. Shaw, R. Szczerba, and J. V. Perea-Calderón,\\ studied with //Spitzer//\\ **[[https://doi.org/10.1088/2041-8205/724/1/L39|Formation of Fullerenes in H-containing Planetary Nebulae]]**,\\ //Astrophys. J.// **724**, Art. No. L39 (2010).\\ Besides several Galactic sources, they also studied LHA 115-N 42, also known as SMP SMC 16, in the Small Magellanic Cloud. Strong features attributed to C<sub>60</sub> were detected near 17.4 and 18.9 μm. These features overlap with weaker features of C<sub>70</sub> in the Galactic PN Tc 1. However, a C<sub>70</sub> feature near 14.8 μm is clearly absent. The 8.5 μm feature of C<sub>60</sub> was also observed weakly, the one near 7.0 μm is overlapped by a much stronger Ar<sup>+</sup> line – similar to the situation in Tc 1. Because of the investigation mentioned above, this identification should be viewed with caution, though it appears to be rather likely. ---- \\ \\ ==== C70 ==== There are no reports on Extragalactic observations of C<sub>70</sub> thus far. ---- Contributor(s): H. S. P. Müller; 06, 2011; 01, 2012 ---- molecules/extragalactic/fullerene_extragalactic.txt Last modified: 2019/10/22 16:32by mueller