Its high-level ionization potential and as the origin of some of the mysterious UIE bands seen in the universe

Is there finally a plausible theoretical basis for the molecular origins and carriers of au minus some of the more prominent so-called “UIE” (Unidentified Infrared Emission) bands that have mystified astronomers for decades?

A team led by LSR Fellow Dr Seyed Abdolreza Sadjadi and LSR Director Professor Quentin Parker in the Department of Physics has now added some interesting theoretical work. It identifies highly ionized species of the famous football-shaped molecule C60 “Buckminsterfullerene” as plausible carriers of at least some of the most important and enigmatic UIE bands that have challenged astronomers since their discovery and study over 16 years.

First, Dr. Sadjadi and Prof. Parker theoretically proved that C60 could survive, in stable states, an ionization up to +26 (which means 30 of the 26 electrons of the buckyball are deleted) before the buckyball disintegrated (Sadjadi & Parker 2021). Now they have shown, by applying the first principles of quantum chemical calculations, what theoretical mid-infrared signatures of these ionized forms of fullerene can be expected. The results are extremely interesting and provocative and could finally point the way to at least a partial resolution of this lingering astrophysical mystery.

Professor Parker said: “I am extremely honored to have played a part in the astonishingly complex quantum chemical research undertaken by Dr. Sadjadi which led to these very exciting results. They concern first the theoretical proof that the fullerene – the carbon 60 – can survive at levels of very high ionizations and now this work shows that the infrared emission signatures of these species perfectly match some of the most important unidentified infrared emission features known. This should help reinvigorate this area of ​​research.

HKU core team found that some of these positively charged fullerenes show strong emission bands that correspond extremely well to the position of the main astronomical emission features UIE at 05,26, 16,21 and 20-21 micrometers (μm). This makes them key target species for the identification of currently unidentified UIE features and provides strong inspiration for future astronomical observations in the mid-infrared wavelength range to test these theoretical findings. They also found that the IR signatures of the group of these cations C60 with q = 1 – 6 are well-separated from the 6.2 μm bands, which are associated with free/isolated aromatic hydrocarbon molecules (called PAH, another potential UIE vector). This greatly facilitates their identification compared to other potential carriers. This discovery is particularly important for the discrimination and exploration of the coexistence of complex organic hydrocarbons and fullerenes in astronomical sources.

Dr Sadjadi said “In our first paper, we theoretically showed that highly ionized fullerenes can exist and survive the harsh and chaotic environment of space. It’s like asking how much air you can push out of a soccer ball and the ball still holds its shape. In this report, we worked with two other eminent astrophysicists and planetary scientists, Prof. Yong Zhang and Dr. Chih-Hao Hsia, both former HKU staff members but still affiliated with LSR, to determine the molecular vibrational ratings of a celestial symphony, i.e. the characteristics that these ionized buckyballs would play/produce. We then searched for them in space, showing that their notes/signatures are easily distinguishable from PAHs.

AstrophysicsBalloonQuantum ChemistryFrench DepartmentFullereneInfraredIonizationPhysics

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