Polycyclic Aromatic Hydrocarbons in Interstellar Chemistry

Interstellar chemistry modifications resulting form the presence of large molecules such as polycyclic aromatic hydrocarbons (PAHs) are investigated. For abundances of PAH relative to hydrogen of greater than 10 to the -8th, free electrons attach to PAH molecules to yield PAH(-) ions, and qualitative interstellar chemistry changes are shown to result as atomic and molecular ions undergo nondestructive mutual neutralization reactions with these negative ions. An increase in the steady state abundances of carbon-bearing molecules is also noted. For a PAH abundance ratio relative to hydrogen of 10 to the -7th, the equilibrium densities of C3H2 and neutral atomic C are found to be enhanced by two orders of magnitude.