During my PhD I have mainly worked on the Aromatic Infrared Bands (AIBs), a family of bands found in dusty galactic and extragalactic environments  illuminated by strong UV field (e.g. planetary nebulae, photodissociation regions, diffuse interstellar medium, post-AGB stars, starburst galaxies...). These bands are universally attributed to a class of molecules called Polycyclic Aromatic Hydrocarbons (PAHs). The mechanism invoked is the absorption of a UV photon followed by relaxation via IR fluorescence. Due to the sensitivity of the mid-IR range to the general structure of the molecule,  not a single PAH molecule has yet been identified in space. My main goal has been to investigate classes of molecules within the PAH family whom contribution to the AIBs could be identified. My method of choice is Density Functional Theory (DFT) which works well for molecules of the size of astronomical PAHs. I perfom vibrational analysis in the double harmonic approximation and compare the results with IR astronomical observations, see for example A. Candian et al, (2012), (2014) or (2015)
Lately we have started to calculate the anharmonic vibrational spectra of small PAHs (up to 5 rings) using Second Order Perturbation Theory (VPT2) to try to understand how anharmonicity affects the vibrational spectra of PAHs. See for example C.J. Mackie, A. Candian et al. (2015),(2016) and E. Maltseva et al. (2015),(2016).

ISO-SWS spectrum of the Orion Bar, a very well known photodissociation region.  Credits: E.Peeters