Failure of hydrogenation in protecting polycyclic aromatic hydrocarbons
  from fragmentation
  A recent study of soft X-ray absorption in native and hydrogenated coronene
cations, C$_{24}$H$_{12+m}^+$ $m=0-7$, led to the conclusion that additional
hydrogen atoms protect (interstellar) Polycyclic Aromatic Hydrocarbon (PAH)
molecules from fragmentation [Reitsma et al., Phys. Rev. Lett. 113, 053002
(2014)]. The present experiment with collisions between fast (30-200 eV) He
atoms and pyrene (C$_{16}$H$_{10+m}^+$, $m=0$, 6, and 16) and simulations
without reference to the excitation method suggests the opposite. We find that
the absolute carbon-backbone fragmentation cross section does not decrease but
increases with the degree of hydrogenation for pyrene molecules.
