Buckminsterfullerene Species Likely the Source of Unidentified Infrared Emission

Conducting quantum chemical calculations, researchers from the University of Hong Kong (HKU), have been able to discover the origin of some mysterious Unidentified Infrared Emission (UIE) bands that have intrigued astronomers for decades. The research links the source of some of these bands to highly ionised football-shaped Buckminsterfullerene C60 or buckyballs. Such bands were first discovered and studied for 30 years and have since kept scientists puzzled over their source. Earlier, researchers had shown that C60 could survive in stable states from being ionised up to +26 before the buckyball disintegrates. Now, in the new study, researchers have applied the first principle of quantum chemical calculations to predict the mid-infrared signatures of the ionised forms of fullerene.

“I am extremely honoured to have played a part in the astonishingly complex quantum chemistry investigations undertaken by Dr Sadjadi that have led to these very exciting results. They concern first with the theoretical proof that Fullerene–Carbon 60–can survive to very high levels of ionisation and now this work shows that the infrared emission signatures from such species are an excellent match for some of the most prominent Unidentified Infrared Emission features known. This should help re-invigorate the area of research,” said professor Quentin Andrew Parker, Director of the LSR in the Department of Physics. Parker is also the author of the study published in The Astrophysical Journal.

The team has noted that some positively charged fullerenes have strong emission bands that substantially match with the position of key astronomical UIE emission features at 11.21, 16.40 and 20-21micrometres (μm).

They offer a great target species for the identification of the UIE bands that have remained unknown so far. In addition, they would also provide strong motivation for more astronomical observations in the future across the mid-infrared wavelength range in order to test the theoretical findings.

The team also observed that the infrared signatures of the group of the C60 cations having q = 1 - 6 are well separated from the 6.2μm bands. The findings are now likely to come in handy for the discrimination and exploration of the coexistence of fullerenes and complex hydrocarbon organics in astronomical sources.