The Aromatic Infrared Bands (AIBs) are a family of emission bands appearing in the infrared (IR) between 3 and 20 µm in spectrum of interstellar regions containing dust and ultraviolet (UV) radiation. Star forming regions, like the nearby Orion Nebula are a perfect example; in there a young star is illuminating with UV photons the dusty cloud where it was born.
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Polycyclic Aromatic Hydrocarbons (PAHs) are molecules made of carbon arranged in a honeycomb structure and decorated with hydroegn. On top of this paragraph you can see Coronene (C H ) while it vibrates.
PAHs are almost universally considered the carriers of the AIBs. They absorb the UV photons coming from the star and re-emit in the infrared. They contain up to 10% of all the carbon present in the Universe.
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In my research I use a combination of computational chemistry methods, experiments, modelling and astronomical observations to study photochemical evolution of PAHs, leading to the variation of the AIB profiles.
The Aromatic Infrared Bands and the PAHs
The Orion Nebula in the Infrared.
The Aromatic Infrared Bands; Peeters et al, 2002
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Interested? Have a look at my article "The Aromatic Universe", that appeared on Physics Today
Below some examples of the research I like to do.
Fragmentation of carbonaceous molecules
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The phenyl cation is the one of the building blocks for PAHs, but little is known about how it fragments. In the paper "IR Photofragmentation of the phenyl cation" ,together with PhD Sandra Wiersma (now postdoc at CNRS, France) and Annemieke Petrignani (University of Amsterdam), we looked at how it fragments with a combination of experiments (infrared multiphoton dissociation or IRMPD spectroscopy) and computational chemistry (Density Functional Theory or DFT). We found out that, unlike other aromatic rings that are prone to H-loss, for this molecule ring-opening and loss of small hydrocarbons is thermodynamically more favorable.
Potential energy surface of phenylium investigated with Density Functional Theory from Wiersma, Candian et al, (2021)
Vibrational spectroscopy of carbonaceous molecules
The largest molecule detected in space is buckminsterfullerene or C both in its neutral and cationic form (Cami et al., 2010; Campbell et al, 2016). One possible way to form C in space is via the fragmentation of PAHs with at least 66 carbon atoms (Zhen et al, 2014). However we know that PAH molecules in space can also be smaller or larger in size (Croiset, Candian et al, 2016). Can then 3D carbon cages be created in space with a similar mechanism? How their infrared spectra would look like? In Candian, Rachid et al (2019), we looked at stability of carbon cages with size between 44 and 70 carbon atoms and calculated their infrared spectra. We concluded that groups of 3D carbon cages can be identied based on their size (large and small), but only very symmetric molecules like C can be unequivocally identified via vibrational spectroscopy.
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