Structural investigation of doubly-dehydrogenated pyrene cations
  The vibrationally resolved spectra of the pyrene cation and
doubly-dehydrogenated pyrene cation (C$_{16}$H$_{10}$$^{.+}$; Py$^+$ and
C$_{16}$H$_{8}$$^{.+}$; ddPy$^+$) are presented. Infrared predissociation
spectroscopy is employed to measure the vibrational spectrum of both species
using a cryogenically cooled 22-pole ion trap. The spectrum of Py$^+$ allows a
detailed comparison with harmonic and anharmonic density functional theory
(DFT) calculated normal mode frequencies. The spectrum of ddPy$^+$ is dominated
by absorption features from two isomers (4,5-ddPy$^+$ and 1,2-ddPy$^+$) with,
at most, minor contributions from other isomers. These findings can be extended
to explore the release of hydrogen from interstellar PAH species. Our results
suggest that this process favours the loss of adjacent hydrogen atoms.
