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

•The electrical discharge of the PAH naphthalene and acetonitrile was investigated by IR-UV ion dip spectroscopy with the free electron laser FELIX in the 550–1800 cm−1 frequency range.•New –CH3 and –CN substituted aromatic species have been identified and their IR spectra characterized.•The NEARIR feature recently implemented in the ORCA software has been used to predict overtones and combination bands.•The results provide insight on new species which could be the object of radio astronomical searches.