Radiation-Induced Transformations of an Isolated C6H6···HCN Complex: Possible Way to Synthesis of Interstellar Benzonitrile.

The recent detection of benzonitrile (C₆H₅CN) in the interstellar medium is one of the most fascinating discoveries in astrochemistry and molecular astrophysics. However, the mechanism of its formation in interstellar ices remains unclear. Here, we report the first evidence for the direct synthesis of benzonitrile through the radiation-induced transformations of an isolated C₆H₆···HCN complex in inert rigid media at cryogenic temperature (4.5 K), as monitored by Fourier transform infrared (FTIR) spectroscopy. The complex was prepared in a solid krypton matrix and characterized by the experimentally observed complexation-induced shifts in the FTIR spectra on the basis of comparison with the results of ab initio calculations. The formation of benzonitrile was revealed through the observation of its three fundamentals and partially confirmed by experiments with deuterated benzene. Presumably, C₆H₅CN results from the dehydrogenation of complex excited states followed by prompt radical-radical recombination within the matrix cage. The proposed route may be relevant to the formation of C₆H₅CN both in the bulky astrophysical ices and on the surface of interstellar dust grains.