Dehydrogenation of polycyclic aromatic hydrocarbons in the diffuse interstellar medium
M. H. Vuong, B. H. Foing;
AaA, 2000, 363, L5
ABSTRACT:We present a model for the hydrogenation states of Polycyclic Aromatic Hydrocarbons (PAHs) in the diffuse interstellar medium.First, we study the abundance of hydrogenation and charge states of PAHs due to photo-ionization, photo-dissociation in the interstellar UV field, electron recombination and chemical reactions between PAH cations and H or H_2.
For PAH cations, we find that the dehydrogenation effects are dominant.
The hydrogenation state of PAHs depends strongly on the H density, the size of molecule and UV field.
In diffuse clouds with low H density and normal UV radiation, PAHs containing less than 40 C are completely or strongly dehydrogenated whereas at high H density, they are normally hydrogenated.
The partially dehydrogenated species dominate in intermediate density clouds.
PAHs above 40 C are quite stable and are fully hydrogenated, which would favor their spectroscopic search in near IR surveys of Diffuse Interstellar Bands (DIBs).
KEYWORDS: ism: molecules, ism: clouds, ism: dust, extinction
PERSOKEY:dust, pah, ,
CODE: vuong2000