  The electronic spectra of gas-phase cationic polycyclic aromatic hydrocarbons
(PAHs), trapped in the Fourier Transform Ion Cyclotron Resonance cell of the
PIRENEA experiment, have been measured by multiphoton dissociation spectroscopy
in the 430-480 nm spectral range using the radiation of a mid-band optical
parametric oscillator laser. We present here the spectra recorded for different
species of increasing size, namely the pyrene cation (C16H10+), the
1-methylpyrene cation (CH3-C16H9+), the coronene cation (C24H12+), and its
dehydrogenated derivative C24H10+. The experimental results are interpreted
with the help of time-dependent density functional theory calculations and
analysed using spectral information on the same species obtained from matrix
isolation spectroscopy data. A kinetic Monte Carlo code has also been used, in
the case of pyrene and coronene cations, to estimate the absorption
cross-sections of the measured electronic transitions. Gas-phase spectra of
highly reactive species such as dehydrogenated PAH cations are reported for the
first time.
