  We present the first infrared (IR) gas phase spectrum of a large and
astronomically relevant PAH cation (C$_{42}$H$_{18}$$^+$, HBC$^+$) and its
di-cation (C$_{42}$H$_{18}$$^{2+}$, HBC$^{2+}$). The spectra are recorded via
infrared multi-photon dissociation (IRMPD) spectroscopy of ions stored in a
quadrupole ion trap, using the intense infrared radiation of a free electron
laser in the 530$-$1800 cm$^{-1}$ (5.6$-$18.9 $\mu$m) range. HBC$^{+}$ shows
main intense absorption peaks at 762 (13.12), 1060 (9.43), 1192 (8.39), 1280
(7.81), 1379 (7.25) and 1530 (6.54) cm$^{-1}$($\mu$m), in good agreement with
DFT calculations that after scaling to take the anharmonicities effect into
account. HBC$^{2+}$ has its main absorption peaks at 660 (15.15), 766 (13.05),
1054 (9.49), 1176 (8.50), 1290 (7.75), 1370 (7.30) and 1530 (6.54)
cm$^{-1}$($\mu$m). Given the similarity in the cationic and di-cationic
spectra, we have not identified an obvious diagnostic signature to the presence
of multiply charged PAHs in space. While experimental issues associated with
the IRMPD technique preclude a detailed comparison with interstellar spectra,
we do note that the strong bands of HBC$^+$ and HBC$^{2+}$ at $\sim$ 6.5, 7.7,
8.4 and 13.1 $\mu$m coincide with prominent aromatic infrared bands (AIBs). HBC
has only trio CH groups and the out-of-plane CH bending mode of both HBC
cations is measured at 13.1 $\mu$m, squarely in the range predicted by theory
and previously found in studies of small (substituted) PAHs. This study
therefore supports the use of AIBs observed in the 11$-$14 $\mu$m range as a
diagnostic tool for the edge topology of large PAHs in space.
