New potential candidates for astronomical searches discovered in the electrical discharge of the PAH naphthalene and acetonitrile

The formation and dissociation mechanisms of polycyclic aromatic hydrocarbons (PAHs) as well as their reactivity with other interstellar molecules are elusive. In this work, we have investigated the electrical discharge chemistry of the PAH naphthalene and acetonitrile, a molecule known to be present in interstellar environments, using a combination of mass-selective IR-UV ion dip spectroscopy with the free electron laser FELIX in the mid-IR frequency region (550 – 1800 cm⁻¹) and quantum chemical calculations. In addition to the species known to be produced in the electrical discharge of pure naphthalene, –CH₃ and –CN substituted unsaturated hydrocarbons have been identified. Most of them, in particular those containing a nitrogen atom in the molecular framework, such as 7H-benzo[7]annulenecarbonitrile, have a substantial dipole moment and, therefore, can be considered as potential candidates for radio astronomical searches. Among the species observed, the two isomers 1- and 2-cyanonaphthalene, which have been recently detected in the TMC-1, have been identified in our experiment, thus continuing to highlight the use of electrical discharge sources as a valuable tool to produce astronomically relevant species.