Presence of N-Graphene in the residue obtained from irradiated benzonitrile ices

Benzonitrile (C₆H₅CN), an aromatic molecule of interest to astrochemists, is reported to be present in the interstellar medium (ISM) [1]. The energetic processing of aromatic molecules can synthesize large and complex aromatic molecules such as the Polycyclic Aromatic Hydrocarbons (PAHs). PAHs are considered to be the carriers of unknown InfraRed (IR) bands. To-date a number of laboratory experiments have reported the formation of complex organics from energetic processing of aromatic molecules [2-3].
In the present investigation, we subjected benzonitrile ice made at 4 K to vacuum ultraviolet (9 eV) radiation. After irradiation the ice was warmed to room temperature, which left a brownish residue on the KBr substrate. The VUV spectrum of the residue is observed to have characteristic aromatic signature. The residue is then transferred to a quantifoil grid for High-Resolution Transmission Electron Microscope (HR- TEM) imaging. HR-TEM micrographs revealed the presence of graphene in the residue. This result suggests that nitrogen-doped graphene (N-graphene) can be synthesized in regions of the ISM where benzonitrile is present.
[1] McGuire et al. (2018) Science, 359 (6372), 202. [2] Callahan et al. (2013) Icarus, 226, 1201. [3] Rahul et al. (2020) Spectrochim. Acta A, 231, 117797.