2015ApJ...798..102W

Studies of interstellar chemistry have grown in number and complexity by both observations and laboratory measurements, and nitrogen-containing aromatics have been implicated as important interstellar molecules. In this paper, the gas-phase collision induced dissociation (CID) processes of protonated pyridazine (1,2-diazine), pyrimidine (1,3-diazine), and pyrazine (1,4-diazine) cations (C₄H₅N₂⁺) are investigated in detail both experimentally and theoretically. The major neutral loss for all three CID processes is HCN, leading to the formation of C₃H₄N⁺ isomers; our density functional theory (DFT) calculations support and elucidate our experimental results. The formation of C₃H₄N⁺ isomers from the reaction of abundant interstellar acrylonitrile (CH₂CHCN) and H⁺is also studied employing DFT calculations. Our results lead to a novel mechanism for interstellar protonated diazine formation from the consecutive reactions of CH₂CHCN+ H⁺ + HCN. Moreover, our results motivate the continuing search for interstellar C₃H₄N⁺ isomers as well as polycyclic aromatic N-containing hydrocarbons (PANHs).