Publication Date:
2014-05-11
Description:
The physical interactions of polycyclic aromatic hydrocarbons (PAHs) with stellar particular radiation are key to understanding the life cycle of PAHs, their abundance and their role in the complex astrochemistry of the interstellar medium. In this context, we present experimental results on the ionization/fragmentation of isolated coronene by a 100-keV proton, reproducing interactions between stellar winds and PAH molecules in the star's environment. In particular, we show, without ambiguity, that such ionization/fragmentation induces intense dehydrogenation processes for which the loss of even numbers of hydrogen atoms and the detection of CH $_2^{+}$ cations as a possible H 2 precursor strongly suggest the formation of H 2 neutral molecules along a scenario revealed by a quantum chemical calculation. We have evaluated the H 2 emission cross-section from the coronene/proton interaction at 100 and 1.6 keV to be 2.97 10 –16 and 3.3 10 –16 cm 2 , respectively. A qualitative discussion on the formation rate of H 2 in the HD 44179 Red Rectangle (RR) nebula leads to the conclusion that such processes could be very efficient, especially inside planetary nebulae rich in PAH molecules interacting with high proton mass-loss rate stars (such as post-asymptotic giant branch stars) or high velocity jets produced by an accretion disc.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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