  Recognized as important interstellar constituents, polycyclic aromatic
hydrocarbons (PAHs) have been intensively studied in astrochemistry and their
spectroscopy, thermodynamics, dynamics, and fragmentations are now amply
documented. There exists typical alternatives to the ground-state regular
planar structures of PAHs, as long as they bear internal energies in the range
1-10 eV. Resulting from intramolecular rearrangements, such high-lying minima
on the potential- energy surfaces should be taken into consideration in the
studies of PAH processing in astrophysical conditions. Resting upon DFT
calculations mainly performed on two emblematic PAH representatives, coronene
and pyrene, in their neutral and mono and multi-cationic states, this second
survey addresses the following alternatives: (1) opened forms containing
ethynyl or 2- butynyl groups, (2) vinylidene isomers, in which phenanthrene
patterns are reorganized into dibenzofulvene ones, (3) twisted forms, where
external CH=CH bonds can be partly twisted, and (4) bicyclobutane forms, in
which the latter are integrated in saturated bicyclic forms. A few scenarios
for elimination of fragments H, H2, C2H2 and C2H4 are explored. As far as
possible, familiar concepts of organic chemistry, such as aromaticity or Clar's
rules, are invoked for interpretations.
