DFT study on interstellar PAH molecules with aliphatic side groups
  Polycyclic Aromatic Hydrocarbon (PAH) molecules have been long adjudged to
contribute to the frequently detected distinct emission features at 3.3, 6.2,
7.7, 8.6, 11.2 and 12.7 {\mu}m with weaker and blended features distributed in
the 3-20 {\mu}m region. The comparatively weaker 3.4 {\mu}m emission feature
has been attributed to have an aliphatic origin as carrier. PAH with aliphatic
functional group attached to it is one of the proposed potential candidate
carriers for the 3.4 {\mu}m emission band, however, the assignment of carrier
is still enigmatic. In this work, we employ Density Functional Theory (DFT)
calculation on a symmetric and compact PAH molecule; coronene (C24H12) with
aliphatic side group to investigate any spectral similarities with observed
features at 3-4 {\mu}m. The side groups considered in this study are -H
(hydrogenated), -CH3 (methyl), -CH2-CH3 (ethyl) and -CH=CH2 (vinyl) functional
groups. Considering the possible presence of deuterium (D) in PAHs, we also
include D in the aliphatic side group to study the spectral behavior. We
present a detailed analysis of the IR spectra of these molecules and discuss
possible astrophysical implications.
